Draw Legend Items With Different Colors in R

  2. HowTo
  3. R Howtos
  4. Draw Legend Items With Different Colors …
Lasha Khintibidze May 26, 2021
R R Plot
  1. Use the legend Function to Add Legend to Plots in R
  2. Use Double legend Call to Draw Legend Items With Different Colors
Draw Legend Items With Different Colors in R

This article will demonstrate how to draw legend items with different colors in R.

Use the legend Function to Add Legend to Plots in R

The legend function is used to draw legend objects on the plots. It takes x and y coordinates as the first two arguments to specify the legend’s position. Although, it can be specified using keywords like: "left", "bottomright", etc. The next parameter is called legend, and it is represented as a vector of characters that need to be displayed in the legend. In this case, we draw lines and points denoted by a triangle or circle shape. Lines and points have different colors, and they need to be displayed in the legend accordingly. The following code snippet draws only shapes and text in the legend.

library(ggplot2)

plot( 0, type = "n", xlim = c(0,5), ylim = c(0,5) )
A <- matrix( c( c(4,1,3,2), c(1,3,4,4)), ncol = 2 )
B <- matrix( c( c(1,4,3,2), c(1,3,1,1)), ncol = 2 )

lines( A, col = "brown" )
points( A, col = "blue", pch = 17 )
lines( B, col = "cyan" )
points( B, col = "purple", pch = 19 )


legend( x = "topleft",
        legend = c("Brown line, blue triangles","Cyan line, purple points"),
        col = c("blue","purple"), lwd = 2, lty = c(0,0),
        pch = c(17,19) )

r plot legend 1

We can also add lines by increasing the values of the lty argument vector. Notice that ones correspond to the straight and uninterrupted line. On the other hand, pch arguments represent the plotting symbols that map to 0:25 integer values and are described in points function documentation.

library(ggplot2)

plot( 0, type = "n", xlim = c(0,5), ylim = c(0,5) )
A <- matrix( c( c(4,1,3,2), c(1,3,4,4)), ncol = 2 )
B <- matrix( c( c(1,4,3,2), c(1,3,1,1)), ncol = 2 )

lines( A, col = "brown" )
points( A, col = "blue", pch = 17 )
lines( B, col = "cyan" )
points( B, col = "purple", pch = 19 )

legend( x = "topleft",
        legend = c("Brown line, blue triangles","Cyan line, purple points"),
        col = c("brown","cyan"), lwd = 1, lty = c(1,1),
        pch = c(17,19), merge = FALSE)

r plot legend 2

Use Double legend Call to Draw Legend Items With Different Colors

The previous example displays the lines and shapes of a single item with the same color. This can be solved by the two invocations of the legend function, each of which displays lines and shapes separately with different colors. Mind though, one of the calls should have empty vector values for the legend parameter.

library(ggplot2)

plot( 0, type = "n", xlim = c(0,5), ylim = c(0,5) )
A <- matrix( c( c(4,1,3,2), c(1,3,4,4)), ncol = 2 )
B <- matrix( c( c(1,4,3,2), c(1,3,1,1)), ncol = 2 )

lines( A, col = "brown" )
points( A, col = "blue", pch = 17 )
lines( B, col = "cyan" )
points( B, col = "purple", pch = 19 )


legend( x = "topleft",
        legend = c("Brown line, blue triangles","Cyan line, purple points"),
        col = c("brown","cyan"), lwd = 1, lty = c(1,1),
       pch = c(NA,NA) )

legend( x = "topleft",
        legend = c("",""),
        col = c("blue","purple"), lwd = 1, lty = c(0,0),
        pch = c(17,19), bty= 'n')

r plot legend 3

Related Article - R Plot