Dr. Mark Gardener

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Index of MonogRaphs

R: MonogRaphs

A series of essays on random topics using R: The Statistical Programming Language

R is a powerful and flexible beast. Getting started using R is not too difficult and you can learn to start using R in an afternoon. However, mastering R takes rather longer! These monographs are my way of exploring various topics in a completely unstructured manner.

Tips & Tricks for R | An Introduction to R| Writer's Bloc | Courses


The 3 Rs:

Reading data
Writing Data
Doing math

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The 3 Rs: Reading, wRiting and aRithmetic

Part 2. Writing

I remember reading about the 3 Rs as the most important topics in education: reading writing and arithmetic. I thought it would be interesting to examine these in an R context e.g. reading data, writing data and doing maths. This page is all about writing, part 1 was about Reading, part 3 will be about aRithmetic. Watch this space...

Index for Part 2.

 

Writing

   

Writing Data Files

Writing Objects

Writing Graphics

Writing Basic Text Formats

Writing Objects to Screen

Copy & Paste Graphics

The write.table() command
The print() command

Save graphics from the GUI

The write.csv() command
The format() command

Device drivers

The write() command
The cat() and paste() commands
Copy a graphics device to disk

Writing Special Format Files

Writing Objects to Disk

Send graphics commands direct to a file
Excel files
Writing Binary Objects

Writing the Console

Other file formats
Writing Text Objects

Writing Scripts

 
Divert console output to disk

Working Directory

Part 1. Reading | MonogRaphs Index | Part 3. aRithmetic


Writing:

Data
Objects
Scripts

Write to disk

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Writing

You can probably categorize the sorts of thing that you can write into four types:

  • Data.
  • R Objects.
  • Graphics.
  • Scripts.

Data is a general term and by this I mean numbers and characters that you might reasonably suppose could be handled by a spreadsheet. Your data are what you use in your analyses.

R objects may be data or other things, such as custom R commands or results. They are usually stored (on disk) in a format that can only be read by R but sometimes they may be in text form.

Graphics are anything that you produce in a separate graphics window, which seems fairly obvious. These items do not appear as regular R objects and have to be treated differently.

Scripts are collections of R commands that are designed to be run "automatically". They are generally saved (on disk) in text format.


Writing basic text formats

Comma separated
use sep = ","

Tab delimited
use sep = "\t"

write.table()
write.csv()
write.csv2()

Use col.names = NA to add an extra item to column headings if needed

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Writing data files

It is useful to be able to write a basic dataset to disk in a standard format that allows it to be opened by different people. The basic distribution of R allows you to save basic text formats easily. If you need to write a proprietary format, such as XLSX you'll need to use additional command packages.

Writing basic text formats

Basic text formats are the most generally useful formats for saving datasets, since they can be handled by the widest range of programs. The comma delimited format (.csv) is the most widely used but Tab and space delimited are also commonly encountered. The workhorse is the write.table() command for this kind of work.

The write.table() command allows you to specify a range of options so you can tailor the output exactly as you want it. However, there are also two convenience commands that help to produce CSV files:

write.csv()
write.csv2()

The write.csv() command gives common defaults that produce basic CSV files, whilst the write.csv2() command produces European style CSV, with commas as decimal point characters and the semi-colon as the delimiter.

The write.table() command

This is the basic command and has a range of options.

wrtie.table(x, file = "", append = FALSE, quote = TRUE, sep = " ",
            eol = "\n", na = "NA", dec = ".", row.names = TRUE,
            col.names = TRUE, qmethod = c("escape", "double"))
x The object to be written; ideally this is a data frame or matrix.
file = ""

The filename in quotes; if blank, the output goes to the current device (usually the screen). Filename defaults to the current working directory unless specified explicitly. Can also link to URL. For Windows and Mac OS the filename can be replaced by file.choose(), which brings up a file browser.

append = FALSE

If the output is a file, append = TRUE adds the result to the file, otherwise the file is overwritten.

quote = TRUE Adds quote marks around text items if set to TRUE (the default).
sep = " " The separator between items (a space), for write.csv the default is "," whilst for write.csv2 it is ";". Specify "\t" for Tab character.
eol = "\n" Sets the character(s) to print at the end of a row. The default, "\n" creates a newline only. Use "\n\r" to mimic Windows endings.
na = "NA" Sets the character string to use for missing values in the data.
dec = "." The decimal point character. For write.csv2 this is ",".
row.names = TRUE

If set to FALSE, the first column is ignored. A separate vector of values can be given to use as row names.

col.names = TRUE

If set to FALSE, the first row is ignored. A separate vector of values can be given to use as column names. If col.names = NA, an extra column is added to accommodate row names (this is the default for write.csv and write.csv2).

qmethod = "escape"

Specifies how to deal with embedded double quote characters. The default "escape" produces a backslash and "double" doubles the quotes.

Using the write.table() command is quite straightforward but you need to be aware of how row names are dealt with. Here is a simple data.frame with two columns and three rows, which are named:

> dat = data.frame(col1 = 1:3, col2 = 4:6)
> rownames(dat) = c("First", "Second", "Third")
> dat
col1 col2
First 1 4
Second 2 5
Third 3 6

The defaults assume that there are both column and row names:

> write.table(dat, file = "") # sends to screen
"col1" "col2"
"First" 1 4
"Second" 2 5
"Third" 3 6

The file may not be read correctly because there are one fewer items in the first row. R will generally read such files okay but your spreadsheet will not. You need to add an extra column to the column names, you do this by specifying col.names = NA like so:

> write.table(dat, file = "", col.names = NA)
"" "col1" "col2"
"First" 1 4
"Second" 2 5
"Third" 3 6

Now you get an extra item in the column headings and the spreadsheet will read thing correctly.


Use write.csv() as a convenience command to save CSV files

Use write.csv2() for European style defaults with semicolon delimiters and commas as decimal point characters

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The write.csv() command

The write.csv() and write.csv2() commands are convenience functions that provide useful defaults that you'd expect to use for writing CSV files. The defaults are set so that the separator is a comma (or semicolon for write.csv2) and the decimal point is a period (or comma for write.csv2). Importantly col.names = NA and row.names = TRUE are set. This means that row names are automatically written and an extra column added to the column names.

If you do not want to write the row names you simply set row.names = FALSE:

> write.csv(dat) # default writes row names and adds to column heading
"","col1","col2"
"First",1,4
"Second",2,5
"Third",3,6
> write.csv(dat, row.names = FALSE) # row names not written
"col1","col2"
1,4
2,5
3,6

In most cases the CSV file is the "go to" format for transferring data to the widest range of computer programs. However, space or Tab delimited are useful for showing data on web pages.


Use write() command to write a vector to screen or disk.

Use write() for matrix objects but row and column names are lost.

You can select the number of columns to write and the separator character.

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The write() command

The write.table() command is designed to deal with 2D objects such as data.frame and matrix items. If you have a simple vector you need a different approach.

The write() command can deal with vector or matrix objects. A matrix is essentially a vector that's been split into rows and columns. However, the write() command cannot handle the row or column names, only the values.

write(x, file = "data",
ncolumns = if(is.character(x)) 1 else 5,
append = FALSE, sep = " ")
x The object to be written, usually a vector or matrix.
file = "data" The filename. If you use "" the output goes to screen.
ncolumns The number of columns required for the output, the default is to use 1 for character data and 5 for numeric.
append = FALSE if TRUE output is added to an existing file.
sep = " " The separator character to use between items, the default is a space. Use "\t" for Tab.
> set.seed(1)
> vec = floor(runif(36, min = 1, max = 100)) > write(vec, file = "") # Defaults to 5 columns for numbers
27 37 57 90 20
89 94 66 63 7
21 18 69 39 77
50 72 99 38 77
93 22 65 13 27
39 2 38 87 34
48 60 49 19 82
67 > write(vec, file = "", sep = "\t", ncolumns = 8) # Use Tab and 8 columns
27 37 57 90 20 89 94 66
63 7 21 18 69 39 77 50
72 99 38 77 93 22 65 13
27 39 2 38 87 34 48 60
49 19 82 67

The write() command is most useful for vector objects without name attributes.


Package xlsx can write Excel format files via:

write.xlsx()

Use append = TRUE to add a new worksheet to an existing file

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Writing special format files

There are occasions when you want to write a data file in a "special" format, the most commonly "requested" format is Excel but you can also write some other formats.

Excel files

To write an Excel file you'll need the xlsx package, which also uses the xlsxjars and rJava packages.

install.packages("xlsx")

If you use the install.packages() command the default will be to get the xlsxjars and rJava packages as well.

The write.xlsx() command is what you'll use most of the time. You specify the object you require and the filename. You can also specify a name for the worksheet and if you use append = TRUE the new worksheet will be added to an existing file.

write.xlsx(x, file, sheetName = "Sheet1, col.names = TRUE,
           row.names = TRUE, append = FALSE, showNA = TRUE)
x The object to be written as an Excel file, usually a data.frame or matrix.
file The filename to use. The output will default to the working directory unless an explicit filepath is used.
sheetName = "Sheet1" The name to give to the worksheet.
col.names = TRUE By default the column names are written to the Excel file.
row.names = TRUE By default the row names are written to the Excel file.
append = FALSE If append = TRUE a new worksheet is added to an existing file.
showNA = TRUE By default NA items appear as #NA in Excel. If showNA = FALSE then NA items appear as blank.

Try the following and then open the Excel file to see the results:

> library(xlsx)
> dat2 = data.frame(col1 = c(1, NA, 3), col2 = 4:6) # data with NA entry
> rownames(dat2) = c("First", "Second", "Third") # set row names

> dat2
col1 col2
First 1 4
Second NA 5
Third 3 6
> write.xlsx(dat2, file = "X1.xlsx", sheetName = "First") # write as Excel
> write.xlsx(dat2, file = "X1.xlsx", sheetName = "Second", append = TRUE, showNA = FALSE) # append worksheet and use blanks for NA

The xlsx package contains other commands to help prepare and write Excel files. I won't deal with them at this point because I want to keep things as simple as possible (I may do a separate monogRaph on the subject). Look at the help index for the package for more details.


Package foreign can write files for SPSS, SAS, Stata and others

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Other file formats

The foreign package allows you to read various file formats. It also allows some to be written back to disk. The package is quite old and probably doesn't support some of the later versions of SPSS for example. You are probably better off saving data as CSV and then using the target program to read the files.


Write to screen

print() links to class attribute. print.default() is used when no class attribute is present.

format() links to class attribute and gives finer control over the display.

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Writing objects

There are several sorts of object you might want to write.

  • General R objects like lists, vectors and so on.
  • Results objects, which can be in form of list, matrix and so on.
  • Custom functions.
  • Graphics.
  • The entire console.

Mostly you'll want to write the objects to disk but there are some useful commands that allow you to write things to the screen.

Writing objects to screen

Generally speaking you can view an R object by typing its name! This shows the "contents" on the screen in a basic form.

The print() command

Typing the object name is really a shortcut for print(object_name). If the object has a class attribute and a print method exists for it, then the object is displayed using the commands in the print method.

Different print methods will have different parameters but the print.default() command will come into operation of no other class attribute is found. Here are the essentials:

print.default(x, digits = NULL, quote = TRUE, print.gap = NULL, right = FALSE)
x The object to be printed.
digits = NULL The number of significant digits to show. The default will depend on the options.
quote = TRUE If TRUE items are shown with quotes.
print.gap = NULL Sets the gap between columns, NULL equates to 1, any integer up to 1024 can be used.
right = FALSE By default text items are left justified.

These parameters give some basic control over the look of the output.

> set.seed(1)
> dat = data.frame(col1 = runif(3), col2 = runif(3))
> rownames(dat) = c("First", "Second", "Third")
> dat # Default output
col1 col2
First 0.2655087 0.9082078
Second 0.3721239 0.2016819
Third 0.5728534 0.8983897 > print(dat, digits = 4) # Significant figures
col1 col2
First 0.2655 0.9082
Second 0.3721 0.2017
Third 0.5729 0.8984
> print(dat, digits = 4, print.gap = 4) # Widen space between columns
col1 col2
First 0.2655 0.9082
Second 0.3721 0.2017
Third 0.5729 0.8984
> print(dat, digits = 4, print.gap = 4, right = FALSE) # Left justify text
col1 col2
First 0.2655 0.9082
Second 0.3721 0.2017
Third 0.5729 0.8984

The print() command gives you some control over the output. It's most important in allowing you to take an object holding a particular class attribute and define a print.xxxx method for that class.

The format() command

Use the format() command to get finer control over the display of objects. The command provides a wider range of options that give you more choice over the result. The command is linked to the class attribute of an object so you can define your own format.xxxx method.

The essentials of the format() command are:

format(x, digits = NULL, justify = "left", width = NULL, scientific = NA)
x The object to be formatted and displayed.
digits = NULL The number of significant figures to display.
justify = "left" How to justify character vectors, "left" (the default), "right" or "centre".
width = NULL The minimum width to use for the columns.
scientific = NA If TRUE the number is displayed in scientific format.
> format(dat, digits = 4, width = 6)
col1 col2
First 0.2655 0.9082
Second 0.3721 0.2017
Third 0.5729 0.8984
> format(dat, digits = 4, width = 8) # Make columns wider
col1 col2
First 0.2655 0.9082
Second 0.3721 0.2017
Third 0.5729 0.8984
> format(dat, digits = 4, width = 8, scientific = TRUE) # Force scientific number format
col1 col2
First 2.655e-01 9.082e-01
Second 3.721e-01 2.017e-01
Third 5.729e-01 8.984e-01

When you have character items you have a bit more control over justification:

> txt = data.frame(Colour = c("Red", "Blue", "Green"),
                   Size = c("Large", "Medium", "Small"))
> format(txt) # The defaults
Colour Size
1 Red Large
2 Blue Medium
3 Green Small
> format(txt, width = 13, justify = "centre") # Wide columns and centered
Colour Size
1 Red Large
2 Blue Medium
3 Green Small
> format(txt, width = 13, justify = "left")
Colour Size
1 Red Large
2 Blue Medium
3 Green Small
> format(txt, width = 13, justify = "right")
Colour Size
1 Red Large
2 Blue Medium
3 Green Small

There are other options available but these essentials will be suitable for many purposes. See the help entry for all the details. See also the prettyNum() command, where you can get much finer control over the display of numbers.


Use cat() to join and print vector objects.

Explicit newlines in cat() with "\n"

Use paste() to join items and convert to character vector.

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The cat() and paste() commands

The cat() command can be used to join items together, which are then printed. Unlike format() or print() the cat() command cannot deal with 2D objects, so you can only use it with vectors.

The strength of the cat() command is in being able to join items together, this allows you to use it to make output messages in custom commands and scripts.

cat(... , sep = " ", fill = FALSE, labels = NULL)

... R objects (including text strings) to be concatenated and printed.
sep = " " The separator character to use between items, the default is a space.
fill = FALSE The width of the output to use. If FALSE only "\n" will create newlines. If TRUE the output is split according to the current width option. If set to a number, this overrides any global width setting.
labels = NULL A vector of labels to use for lines of the output.
> cat(dat$col1, dat$col2)
0.2655087 0.3721239 0.5728534 0.9082078 0.2016819 0.8983897
> cat(dat$col1, dat$col2, fill = 30, sep = "-")
0.2655087-0.3721239-0.5728534-
0.9082078-0.2016819-0.8983897
> cat(dat$col1, dat$col2, fill = 20, sep = ",", labels = letters[1:5])
a 0.2655087,
b 0.3721239,
c 0.5728534,
d 0.9082078,
e 0.2016819,
a 0.8983897

Use "\n" to generate explicit newlines. If you want to use the name of an R object you must wrap it in a deparse(substitute()) command, otherwise the command will attempt to output the object, rather than its name:

> cat("\n", "Your data:\n", deparse(substitute(dat)))

 Your data:
dat > cat(dat)
Error in cat(list(...), file, sep, fill, labels, append) :
argument 1 (type 'list') cannot be handled by 'cat'

The paste() command joins items together but doesn't do anything else with the object other than converting to a character vector. You can use it in conjunction with cat() or other commands to produce output.

paste(... , sep = " ", collapse = NULL)

... R objects to be concatenated.
sep = " " The character to use is separating the items, the default is a space.
collapse = NULL The output is collapsed to form a single vector, separated by the character you specify instead of NULL.

The items are combined element by element; here is a data.frame as an example:

> dat
col1 col2
First 1 4
Second 2 5
Third 3 6
> paste(letters[1:3], dat$col1)
[1] "a 1" "b 2" "c 3"
> paste(dat$col1, dat$col2, sep = "**")
[1] "1**4" "2**5" "3**6" > paste(dat$col1, dat$col2, sep = "-", collapse = " ")
[1] "1-4 2-5 3-6"

You can also use the write() command to send output to the screen, see the details from the earlier section. The only difference is that you specify file = "" instead of an explicit filename.


Write binary files to disk

Use save() to save one or more R objects to disk as binary files.

Use save.image() to save all R objects to disk as binary files.

Write text representations of objects to disk

Use dput() to write a single object and dget() to read it back.

Use dump() to write several objects and source() to read them back.

Other commands
cat()
write()
write.table()

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Writing objects to disk

Any R object can be saved onto disk in a format that allows R to open it later. Some R objects can be saved in text format and retrieved later.

Writing binary objects

Any R object can be saved to disk. The basic command to do this is save(). You simply provide the names of the objects you want to save (separated by commas) and the filename for the target file.

save(..., file)

You can also use a list of names instead of specifying them explicitly. This means you could use another command to make your list, for example:

save(list = ls(), file = "my_objects.RData")

The save.image() command is a convenience command that essentially uses list = ls() to save all the objects.

save.image(file = "my_stuff.RData")

If you leave the filename empty and use save.image() this is essentially what you get when you quit R and say "yes" when asked if you want to save the workspace.

Writing text objects

R objects can also be saved in text form. You can see how to save data files, such as data.frame and matrix objects using write.table(). You can save vector and matrix objects using the write() command. Other objects can be more tricky to represent as text. R has a couple of commands that make ASCII representations of objects (as far as possible), which can be read by humans and restored to R.

dput()
dump()

The main difference between the two commands is that dput() writes a single object, whilst dump() can write several objects and append them to an existing file.

dput(x, file = "")

The dput() command attempts to write an ASCII representation of the object. This is human-readable, but not in a spreadsheet like form. To get an object back to R use dget().

> dat
col1 col2
First 1 4
Second 2 5
Third 3 6
> dput(dat, file = "")
structure(list(col1 = 1:3, col2 = 4:6), .Names = c("col1", "col2"), row.names = c("First", "Second", "Third"), class = "data.frame")

You can see that the object looks more like a set of R commands (which essentially, it is).


dump(list, file = "dumpdata.R", append = FALSE, control = "all")

list An object containing the names of the objects to be written. You can also use a command that produces a vector of names.
file = "dumpdata.R" The filename to use. To send to screen use file = "".
append = FALSE If TRUE the objects (as text) are appended to an existing file.
control = "all" Sets deparsing control. Use control = NULL to skip many of the object attributes.

The dump() command requires a list of names as a character vector; you can use a command that will produce a character vector (such as the ls() command) instead of explicit names.

> dat
col1 col2
First 1 4
Second 2 5
Third 3 6
> dump("dat", file = "")
dat <-
structure(list(col1 = 1:3, col2 = 4:6), .Names = c("col1", "col2"
), row.names = c("First", "Second", "Third"), class = "data.frame")
> dump(ls(pattern = "dat"), file = "", control = NULL)
dat <-
list(col1 = 1:3, col2 = 4:6) > dump(c("mat", "dat"), file = "")
mat <-
structure(c(27, 37, 57, 90, 20, 89, 94, 66, 63, 7, 21, 18, 69,
39, 77, 50, 72, 99, 38, 77, 93, 22, 65, 13, 27, 39, 2, 38, 87,
34, 48, 60, 49, 19, 82, 67), .Dim = c(6L, 6L))
dat <-
structure(list(col1 = 1:3, col2 = 4:6), .Names = c("col1", "col2"), row.names = c("First", "Second", "Third"), class = "data.frame")

Note that using control = NULL strips out most of the attributes. However, if you want to read the object into R (using the source() command) you'll need to preserve as many attributes as possible.


You can also use the cat() command to join items together and then send the result to disk. You simply supply an explicit filename to the file parameter.


Use sink() or
capture.output() to divert console output to disk

More about sending R output to disk files on the Tips & Tricks page

Tips & Tricks Index

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Divert console output to disk

Sometimes it is useful to be able to divert the output that would normally appear on screen to a disk file. For example, results of analyses such as analysis of variance and regression produce a table-like output. These results can be "ported" to disk files with the sink() or capture.output() commands.

The sink() command allows you to send anything that would have gone to the console (your screen) to a disk file instead.

sink(file = NULL, append = FALSE, split = FALSE)

You need to supply the filename, setting file = NULL closes the connection and stops sink()ing. To add to an existing file use append = TRUE. If you set split = TRUE the output goes to the console and the file you specified.

When you issue the command a file is created, ready to accept the output. If you set append = FALSE and the file already exists, it will be overwritten. If you set file = TRUE a connection is opened and subsequent output goes to the file.

> sink(file = "Out1.txt", split = TRUE, append = FALSE) # Send output to screen and file

> summary(lm(Fertility ~ . , data = swiss))

Call:
lm(formula = Fertility ~ ., data = swiss) Residuals:
Min 1Q Median 3Q Max
-15.2743 -5.2617 0.5032 4.1198 15.3213 Coefficients:
Estimate Std. Error t value Pr(>|t|)
(Intercept) 66.91518 10.70604 6.250 1.91e-07 ***
Agriculture -0.17211 0.07030 -2.448 0.01873 *
Examination -0.25801 0.25388 -1.016 0.31546
Education -0.87094 0.18303 -4.758 2.43e-05 ***
Catholic 0.10412 0.03526 2.953 0.00519 **
Infant.Mortality 1.07705 0.38172 2.822 0.00734 **
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 Residual standard error: 7.165 on 41 degrees of freedom
Multiple R-squared: 0.7067, Adjusted R-squared: 0.671
F-statistic: 19.76 on 5 and 41 DF, p-value: 5.594e-10 > sink(file = NULL) # Stop sending output to file

Note that even if you set append = FALSE subsequent output is appended to the file. Once you issue the command sink(file = NULL) output stops and you can see your file using any kind of text editor.

Output from sink() command in a text file
Output from the console ported to a text file using the sink() command.

If you only want to send a single "result" to a disk file you can use the capture.output() command instead.

capture.output(..., file = NULL, append = FALSE)

You provide the commands that will produce the output and the filename. If you set append = TRUE and the target file exists, the output will be added to the file. If you set append = FALSE (the default) the file will be "blanked" and the output will therefore overwrite the original contents.

Note that there is no equivalent of the split argument, all output goes to the file and cannot be "mirrored" to the console. You can supply several commands, separated by commas.

> capture.output(ls(), search(), file = "Out1.txt")

This example sent the ls() command followed by search(), with the results being output to the disk file.

Once you have your output in a text file you can transfer it to your word processor with a little pre-processing via Excel. See more about this on my Tips & Tricks page.


Write the console to a text file using the GUI in Windows or Mac

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Writing the console

You can save the entire console output from the GUI if you have Windows or Mac OS:

  • Mac: File > Save
  • Windows: File > Save to File

The result is a plain text file that mimics the console, whatever appears in your console will end up in the file.


Graphics can be copied to clipboard or saved to disk from the GUI.

Graphic device drivers allow you to save a graphic to disk, you can copy a graphic window or send graphics commands direct to disk file.

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Writing Graphics

R has extensive graphical capabilities and there are many commands that will create graphics, which appear in graphical windows. These graphics are separate from the console. You can write an R graphical object into a disk file in one of several ways:

  • Copy and Paste to a different program (such as a word processor).
  • Save the graphic from the GUI, as a graphics file (e.g. PNG, JPG, PDF).
  • Use the device drivers to copy a graphic from the graphic window to a disk file.
  • Use the device drivers to channel graphical commands directly to a disk file.

The route you take will depend largely on the quality of the final graphic you want. Copy and Paste will work quite well for many purposes but for high quality images you'll need to use the device drivers. It is possible to save a graphic direct to disk from Windows or Mac GUI but the quality is limited to 72dpi.


Use the GUI to copy/paste or save graphics.

72 dpi is the max resolution via the GUI

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Copy & Paste Graphics

You can simply select the graphics window in R and copy to the clipboard. The clipboard can be pasted into most programs and be recognized as a graphic.

  • On a Mac the graphic will be copied as a PDF object.
  • On Windows you can choose to copy the graphic as a bitmap (Ctrl+C, the default) or as a metafile (Ctrl+W).

Copying an R graphic to the clipboard
In Windows you can copy an R graphic to the clipboard in alternative formats

In any event the graphic is transferred to your current application as a graphic. The quality of image will depend somewhat on your computer settings but is generally suitable for most daily purposes.

Save graphics from the GUI

You can also save a graphic directly from R using the GUI (assuming you are using Windows or Mac). A browser window opens, allowing you to send the file to a location of your choosing.

  • On a Mac the file will be saved as a PDF.
  • On Windows you can select a file type, there are several options.

Saving an R graphic in Windows, there are several options for format
Saving an R graphic in Windows allows various file formats

The quality of your image (the image size) will depend upon your system settings but you'll only achieve 72 dpi as a resolution. If you need high-quality images then you need to use the device drivers.


Use device drivers to copy a graphic or send commands to a disk file.

Graphics devices:

bmp()
png()
jpeg()
tiff()
pdf()

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Device Drivers

The device drivers enable you to send graphics commands directly to a file, rather than the screen. In this way you are able to produce graphics in various formats, with much higher resolution. You can use the device drivers in two main ways:

  • To write an existing graphics window to a file.
  • To write graphics commands direct to a file.

The most commonly used device drivers correspond to popular graphics formats, here are the essentials:

  • bmp(width = 480, height = 480, units = "px", bg = "white", res)
  • jpeg(width = 480, height = 480, units = "px", quality = 75, bg = "white", res)
  • png(width = 480, height = 480, units = "px", bg = "white", res)
  • tiff(width = 480, height = 480, units = "px", compression, bg = "white", res)

You specify the size of the graphic as width and height. The default is to treat these measurements as pixels, but you can specify units as pixels, inches, centimetres or millimetres. The resolution can be specified, so setting res = 300 will give 300 dpi.

For jpeg you can specify the quality, this sets the approximate percentage filesize so 25 is a smaller file with more compression than 75.

For tiff you can specify a compression, the options are, "none", "rle", "lzw", "jpeg" or "zip".

You can also make pdf using the pdf() device driver:

pdf(height = 7, width = 7, onefile, paper, colormodel)

For pdf you specify the size in inches. The onefile parameter allows multiple plots to be sent to one file (as separate pages). You can also specify the target page size. The colormodel parameter allows you to specify the colour encoding, the default is "srgb" but you can specify "gray" or "cmyk".


Use dev.print() to send a graphic window to disk and "close" the file.

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Copy a graphics device to disk

If you have produced a graphic, in a regular graphic window, and want to save it as a high quality file you can use one of two commands:

dev.copy()
dev.print()

You specify a filename and the type of device you want to make, for example:

> set.seed(22) # set random number seed
> ## Now make a plot
> boxplot(rnorm(20), rpois(20, 1),
names = c("norm", "poisson"),
las = 1, col = "gray90") > ## Send to file as PNG
> dev.print(device = png, file = "Myplot.png",
height = 512, width = 512)
quartz
2

Graphic saved using dev.print()
A graphics window sent to a file as a PNG using dev.print()

 

If you use dev.print() the file is written and immediately "closed". If you use dev.copy() the file it written but not "closed", which allows you to send additional commands to the file, which must be "closed" using the dev.off() command.

> set.seed(11) # Set random number seed
> ## Make a plot
> boxplot(rnorm(20), rpois(20, 1),
names = c("norm", "poisson"),
las = 1, col = "gray90") > ## Copy to a file as PNG
> dev.copy(device = png, file = "Myplot.png",
height = 512, width = 512, res = 150)
quartz_off_screen
3 > ## Add more graphics commands, which go to file not on-screen graphic
> title("Title added later") > ## Close graphic file and finish
> dev.off()
quartz
2

Graphic saved to file using dev.copy()
A graphics window saved to file using dev.copy() allows additional graphics commands to be added.
The file is finished and closed using dev.off()

Note that in the preceding example the resolution was set to 150, which affected the size of the text relative to the graphic elements. If you wanted to keep the same relative size as before, set height and width to 512*150/72.

Note that PNG files have the background set to "transparent". If you want to have a plain white background you will need to specify this explicitly in the original graphical command(s) before you use dev.print() or dev.copy(). The simplest way is to set the default:

par(bg = "white")

Now any PNG files you produce will have a white background. Reset to transparent in the same manner.

Use dev.copy() to send a graphic to disk and allow additional graphics commands to be sent to the file. Finish with dev.off()

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Send graphics commands direct to a file

If you want to send graphics direct to disk as files you simply issue the appropriate device instruction, which you follow with the graphics commands. Close out the file with dev.off().

> jpeg(file = "MyJpeg.jpg") # Prepare a jpeg file using the defaults
> set.seed(33) # Set random number seed > ## Make a boxplot, the graphics go direct to file
> boxplot(rnorm(20), rpois(20,1),
names = c("norm", "poisson"),
las = 1, col = "cornsilk")
> dev.off() # Finish and close the file
quartz
2

A jpeg written directly to file
When you send graphics commands direct to disk you start the device driver,
then issue graphics commands and finally close the file (this is a jpeg).


The pdf() device can send multiple plots to a single file.

Use onefile = FALSE to make multiple plots in separate files.

Set paper size using paper parameter, defaults to graphic size (7").

Use family parameter to set different font family.

Fonts are not embedded.

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PDFs are handled generally in the same manner but the parameters are slightly different. Resolution is not an issue so you specify the height and width in inches.

By default multiple plots are sent to a single file, as separate pages. The default page size ("special") is set to the same as the graphic size (height and width both 7" default) but you can specify alternatives, paper = :

  • "a4" or "A4"
  • "letter"
  • "legal" or "us"
  • "executive"

Landscape orientation can be achieved"

  • "A4r"
  • "USr"

These can all be capitalised.

It is possible to change the font(s) used in the file by setting the family parameter. By default fonts are not embedded so it is best to stick to basic ones e.g.

  • "Helvetica" – the default
  • "AvantGarde"
  • "Bookman"
  • "Courier"
  • "Helvetica-Narrow"
  • "NewCenturySchoolbook"
  • "Palatino"
  • "Times"
## Set PDF to single file using Bookman font family
> pdf(file = "MyPDF.pdf", family = "Bookman")

## Make a couple of plots
> boxplot(rnorm(20), rpois(20,1), names = c("norm", "poisson"), las = 1, col = "cornsilk")
> boxplot(rnorm(20), rpois(20, 1), names = c("norm", "poisson"), las = 1, col = "gray90")
## Close the file and finish > dev.off()
pdf
3

The preceding example should produce two boxplots in a single file. The size of the paper will be the default (7"). The Bookman font family was used.


Use a C integer format index in the filename for multiple plots

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Multiple plot files

If you want to produce multiple plots it is not necessary to issue a separate filename for each plot. You can simply add an index to the filename; something like %03d will produce three-digit integer values in the filename:

## Start a jpeg device with default size but an indexed name
> jpeg(file = "MyJpeg%03d.jpg")

## Make a plot
> boxplot(rnorm(20), rpois(20, 1),
names = c("norm", "poisson"),
las = 1, col = "gray90")
## Add a title > title(main = "Fig. 1") ## Start a new plot, this closes the previous
> boxplot(rnorm(20), rpois(20,1), names = c("norm", "poisson"), las = 1, col = "cornsilk")
> title(main = "Fig. 2") ## Close the last device and finish the file
> dev.off()
null device
1

The preceding example should produce two plots, one called MyJpeg001.jpg and another MyJpeg002.jpg. Note that the first file is "closed" when you issue a graphical command that would create a new plot. So if you want to add titles or similar, then you should do it before starting the next graphic, you cannot go back.


Write scripts in any text editor.

Windows and Mac have built-in editor.

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Writing scripts

A script is simply a text file containing a series of R commands. You store the file and run it using the source() command. You have two main choices for writing of script files: use the built-in script editor or an outside editor. The GUI for Windows and Mac incorporates a script editor but only the Mac supports syntax highlighting.

To start a new script:

Win: File > New script
Mac: File > New Document

You can write a script in any text editor of course. In Windows the Notepad++ program is a simple editor with syntax highlighting. On the Mac the TextWrangler program is highly recommended. On Linux there are many options, the default text editor will often support syntax highlighting, Geany is one IDE that has syntax highlighting and integrates with the terminal.

The RStudio IDE is very capable and makes a good platform for using R for any OS. The script editor has syntax highlighting.


Output defaults to the working directory.

View working directory with getwd() and set with setwd()

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Working Directory

R uses a working directory, where it stores files and where it looks for items to read. You can see the current working directory using getwd():

> getwd()
[1] "/Users/markgardener" > getwd()
[1] "C:/Users/Mark/Documents"

So, whenever you specify a filename it will be output to the working directory unless you specify a "complete" location, that is the full directory path. There is more about the working directory in the page about Reading.


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