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ggplot2: Overplotting In a Faceted Scatterplot

December 3, 2009

Hadley Wickham recently shared a nice tip on how to get a faceted scatterplot plot with all points in the background of each plot.

This technique makes a clever use of setting the faceting variable to NULL so that all points are plotted in light grey in all the facets.

> library(ggplot2)
> ggplot(mtcars, aes(cyl, mpg)) + geom_point(data = transform(mtcars,
     gear = NULL), colour = "grey80") + geom_point() +
     facet_grid(~gear) + theme_bw()
overplotting-004.png

Update 17 May 2010

bch asked in the comments below, how to achieve the same when there are two facets. The method is the same, now one would need to exclude both of the facetting variables from the dataset used to draw the light grey points.

> ggplot(mtcars, aes(cyl, mpg)) + geom_point(data = mtcars[,
     !names(mtcars) %in% c("am", "gear")],
     colour = "grey80") + geom_point() + facet_grid(am ~
     gear) + theme_bw()
overplotting-006.png
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3 Comments leave one →
  1. efrique permalink
    December 4, 2009 1:47 pm

    Oh, that’s nice.

  2. bch permalink
    May 17, 2010 8:59 pm

    This is great, thank you! Do you happen to know if there is a way to do this when there is two facets? e.g., facet_grid(x~y)?

    Thanks!

    • learnr permalink*
      May 17, 2010 10:11 pm

      Yes it is possible – I have updated the post.

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