geom_point Legend with Custom Colors in ggplot

March 7, 2013
By

(This article was first published on Mollie's Research Blog, and kindly contributed to R-bloggers)

Formerly, I showed how to make line segments using ggplot.

Working from that previous example, there are only a few things we need to change to add custom colors to our plot and legend in ggplot.

First, we’ll add the colors of our choice. I’ll do this using RColorBrewer, but you can choose whatever method you’d like.

library(RColorBrewer)
colors = brewer.pal(8, "Dark2")

The next section will be exactly the same as the previous example, except for removing the scale_color_discrete line to make way for the scale_color_manual we’ll be adding later.

library(ggplot2)

data <- as.data.frame(USPersonalExpenditure) # data from package datasets
data$Category <- as.character(rownames(USPersonalExpenditure)) # this makes things simpler later

ggplot(data,
  aes(x = Expenditure,
    y = Category)) +
labs(x = "Expenditure",
  y = "Category") +
geom_segment(aes(x = data$"1940",
    y = Category,
    xend = data$"1960",
    yend = Category),
  size = 1) +
geom_point(aes(x = data$"1940",
    color = "1940"), # these can be any string, they just need to be unique identifiers
  size = 4,
  shape = 15) +
geom_point(aes(x = data$"1960",
    color = "1960"),
  size = 4,
  shape = 15) +
theme(legend.position = "bottom") +

And finally, we’ll add a scale_color_manual line to our plot. We need to define the name, labels, and colors of the plot.

scale_color_manual(name = "Year", # or name = element_blank()
  labels = c(1940, 1960),
  values = colors)

And here’s our final plot, complete with whatever custom colors we’ve chosen in both the plot and legend:

geom_point in ggplot with custom colors in the graph and legend

I’ve updated the gist from the previous post to also include a file that has custom colors.

To leave a comment for the author, please follow the link and comment on their blog: Mollie's Research Blog.

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