Dr. Mark Gardener


Providing training for:

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Tips and Tricks - for R and Excel

On these pages you can find tips, tricks and hints for using both R and Excel. At the end of each tip there are links forwards and backwards as appropriate. There is also an index of R tips and an index of Excel tips.

For most analytical purposes the combination of Excel and R is unbeatable! Excel is great as a data management tool and for preparing data for analysis. You can also use it to get an overview of your data or to make simple (and not so simple) graphs. R is an analytical "swiss army knife" and can carry out a mind-boggling array of analytical routines as well as producing great graphics.

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

Transparent colors are made easily in R using rgb()

Add alpha = n to make colors transparent (larger n = less transparent)


Make transparent colors

You can easily make transparent colors using R and the rgb() command. These colors can be useful for charts and graphics with overlapping elements.

The rgb() command is the key: you define a new color using numerical values (0–255) for red, green and blue. In addition you set an alpha value (also 0–255), which sets the transparency (0 being fully transparent and 255 being "solid").

You also need to set the maximum color value, so that the command can relate your alpha value to a level of transparency. In practice setting max = 255 works well (since RGB colors are usually defined in the range 0–255).

The following example takes the standrard blue and makes it transparent (~50%):

mycol <- rgb(0, 0, 255, max = 255, alpha = 125, names = "blue50")

Note that the names parameter sets a name attribute for your color. You cannot use the name directly but it can be useful to see a name, e.g.

> mycol

Use col2rgb() to get RGB components of one or more colors


Get the RGB values

Use the col2rgb() command to get the red, green and blue values you need for the rgb() command e.g.:

> col2rgb("lightblue")
red 173
green 216
blue 230

This gives you a matrix with three rows (red, blue, green). This means you can get values for several colors at once:

> col2rgb(c("lightblue", "lightgreen", "pink"))
[,1] [,2] [,3]
red 173 144 255
green 216 238 192
blue 230 144 203

A custom function to create transparent colors...


Custom function for transparent colors

It is fairly easy to make a custom function that takes a named color and makes a transparent version. Here is some code that makes a single color. It could be extended to make a matrix of several colors quite easily:

## Transparent colors
## Mark Gardener 2015
## www.dataanalytics.org.uk
  t_col <- function(color, percent = 50, name = NULL) {
#	  color = color name
#	percent = % transparency
#	   name = an optional name for the color
## Get RGB values for named color
  rgb.val <- col2rgb(color)
## Make new color using input color as base and alpha set by transparency
  t.col <- rgb(rgb.val[1], rgb.val[2], rgb.val[3],
               max = 255,
               alpha = (100-percent)*255/100,
               names = name)
## Save the color

## END


Here is a quick example of the function in action:

> opar <- par(mfrow = c(1,2))
> set.seed(1)
> hist(rnorm(100), col = "pink")
> mycol <- t_col("pink", perc = 50, name = "lt.pink")
> hist(rnorm(100), col = mycol)
> par(opar)

Example of transparent color
The histogram on the right uses a transparent color; not really evident unless colors overlap

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An introduction to R

See my Publications about Excel, R, statistics and data analysis Courses in R, data analysis, data management and statistics Visit the R Project website

See my Publications about statistics and data analysis.

MonogRaphs: random topics in R

Writer's Bloc – my latest writing project includes R scripts

Courses in data analysis, data management and statistics.

My Publications about statistics and data analysis

Managing Data Using Excel, Cover

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