ggplot: colour points by groups based on user defined colours

color-codes, colors, ggplot2, r, scatter-plot

Solution

You are somewhere between two different solutions.

One approach is to not put the colors into the `df` data frame and specify the mapping between `zone` and desired color in the scale call:

ggplot(data=df, aes(col, D, colour = zone))+ 
  geom_point() +
  scale_colour_manual(values=setNames(color.codes, zone))

Note that this does not use `color.codes` or `color.names` from `df`, nor does it use `df2` directly (though it does use the columns that are used to make `df2`; if you have something like `df2` and not the columns separately, you can use `setNames(df2$color.codes, df2$zone)` instead).

The other approach maps color directly to the color codes and uses `scale_color_identity`, but then has to go through some additional labeling to get the legend right.

ggplot(data=df, aes(col, D, colour = color.codes)) +
  geom_point() +
  scale_colour_identity("zone", breaks=color.codes, labels=zone, guide="legend")

The first is, in my opinion, the better solution.

Problem

I am trying to define the colours of groups of points plotted in ggplot. I adapted code from this post: Color ggplot points based on defined color codes but as soon as I have more than one row defined by the same grouping variable (rather than a separate colour for each row), the code fails, and I can't figure out why. Below is a reproducible example: ``` #create some data zone <- c("E","E","C","C","C","E","E") #grouping variable col <- c(50,100,150,200,250,300,350) #x variable D <- c(.4,.45,.20,.22,.30,.31,.35) #y variable df1 <- data.frame(zone, D, col); df1 #create a colour scheme based on grouping variable 'zone' zone <-c("E","C") color.codes<-as.character(c("#3399FF", "#FF0000")) color.names<-c("blue", "red") df2=data.frame(zone, color.codes, color.names); df2 # merge color specifications with data df <-merge(df1,df2, by=("zone"), all.x=TRUE, all.y=TRUE); df ``` The data then look like this: ``` zone D col color.codes color.names C 0.20 150 #FF0000 red C 0.22 200 #FF0000 red C 0.30 250 #FF0000 red E 0.40 50 #3399FF blue E 0.45 100 #3399FF blue E 0.31 300 #3399FF blue E 0.35 350 #3399FF blue ``` The goal is to produce a plot where points in zone 'C' are red and those in 'E' are blue, but using the code from the example cited everything is plotted in red: ``` p <- ggplot(data=df, aes(col, D, colour = zone))+ geom_point() p + scale_colour_manual(breaks = df$zone, values = df$color.codes) ``` Can anyone see the fatal flaw, why this code won't work across groups in this way? Thanks so much in advance

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