Beginner's guide to R: Painless data visualization

Part 4 of our hands-on guide covers simple graphics, bar graphs and more complex charts.

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For many more details, check the help command on a palette such as:

?rainbow

   Using color
Using three colors in the R rainbow palette.

Now that you've got a list of colors, how do you get them in your graphic? Here's one way. Say you're drawing a 3-bar barchart using ggplot() and want to use 3 colors from the rainbow palette. You can create a 3-color vector like:

mycolors <- rainbow(3)

Or for the heat.colors pallette:

mycolors <- heat.colors(3)

Now instead of using the geom_bar() function without any arguments, add fill=mycolors to geombar() like this:

ggplot(mtcars, aes(x=factor(cyl))) + geom_bar(fill=mycolors)

You don't need to put your list of colors in a separate variable, by the way; you can merge it all in a single line of code such as:

ggplot(mtcars, aes(x=factor(cyl))) + geom_bar(fill=rainbow(3))

But it may be easier to separate the colors out if you want to create your own list of colors instead of using one of the defaults.

The basic R plotting functions can also accept a vector of colors, such as:

barplot(BOD$demand, col=rainbow(6))

You can use a single color if you want all the items to be one color (but not monochrome), such as

barplot(BOD$demand, col="royalblue3")

Chances are, you'll want to use color to show certain characteristics of your data, as opposed to simply assigning random colors in a graphic. That goes a bit beyond beginning R, but to give one example, say you've got a vector of test scores:

testscores <- c(96, 71, 85, 92, 82, 78, 72, 81, 68, 61, 78, 86, 90)

You can do a simple barplot of those scores like this:

barplot(testscores)

And you can make all the bars blue like this:

barplot(testscores, col="blue")

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