Mix color and fill aesthetics in ggplot

Question

I wonder if there is the possibility to change the fill main colour according to a categorical variable

Here is a reproducible example

df = data.frame(x = c(rnorm(10, mean = 0),
                  rnorm(10, mean = 3)),
            y = c(rnorm(10, mean = 0),
                  rnorm(10, mean = 3)),
            grp = c(rep('a', times = 10),
                    rep('b', times = 10)),
            val = rep(1:10, times = 2))

ggplot(data = df,
       aes(x = x,
           y = y)) +
  geom_point(pch = 21,
             aes(color = grp,
                 fill = val,
                 size = val))

Of course it is easy to change the circle colour/shape, according to the variable grp, but I'd like to have the a group in shades of red and the b group in shades of blue. I also thought about using facets, but don't know if the fill gradient can be changed for the two panels.

Anyone knows if that can be done, without gridExtra?

Thanks!

You could try to plot first group in blue as it is, then add whole new layer like: `+geom_point(data=df[group==b],aes(...),fill=val, col="red")` roughly :) so idea (most likely suboptimal) is to plot new data from new data and then set the colour to be red.. — Jan Sila, Aug 11 '16 at 11:11
Not working: the `col` argument defines the color of the shape, not the main fill theme — Emiliano, Aug 11 '16 at 11:18

score 3 · Answer 1 · edited May 23 '17 at 12:32

I think there are two ways to do this. The first is using the alpha aesthetic for your val column. This is a quick and easy way to accomplish your goal but may not be exactly what you want:

ggplot(data = df,
       aes(x = x,
           y = y)) +
  geom_point(pch = 21,
             aes(alpha=val,
                 fill = grp,
                 size = val)) + theme_minimal()

The second way would be to do something similar to this post: Vary the color gradient on a scatter plot created with ggplot2. I edited the code slightly so its not a range from white to your color of interest but from a lighter color to a darker color. This requires a little bit of work and using the scale_fill_identity function which basically takes a variable that has the colors you want and maps them directly to each point (so it doesn't do any scaling).

This code is:

#Rescale val to [0,1]
df$scaled_val <- rescale(df$val)
low_cols <- c("firebrick1","deepskyblue")
high_cols <- c("darkred","deepskyblue4")

df$col <- ddply(df, .(grp), function(x)
  data.frame(col=apply(colorRamp(c(low_cols[as.numeric(x$grp)[1]], high_cols[as.numeric(x$grp)[1]]))(x$scaled_val),
                       1,function(x)rgb(x[1],x[2],x[3], max=255)))
)$col
df

ggplot(data = df,
       aes(x = x,
           y = y)) +
  geom_point(pch = 21,
             aes(
                 fill = col,
                 size = val)) + theme_minimal() +scale_fill_identity()

The former solution is genial, and perfectly in line with the ggplot2 style. However it makes me wonder what would happen whit different ranges of val, say 1-10 for grp = a and 20-50 for grp = 50. Of course, comparing similar objects, this shouldn't happen and, if so, that would be a correct visualization. Another "issue" might be the absence of a legend: here you use the size as proxy of the fill (alpha) value. The very same problem you have in the second option, since using `guide = 'legend'` returns the entire list of hexadecimal values in the column `df$col`. — Emiliano, Aug 11 '16 at 14:29
I'm using the `size` since you use it in your original code. It can easily be removed. In terms of the legend, what you're trying to do is not encouraged by `ggplot` (hence why its so hard to do) so if you wanted to do the latter, you would likely need to override the legend aesthetic or create one on your own - either way its very manual — Mike H., Aug 11 '16 at 14:42

score 1 · Answer 2 · edited May 23 '17 at 12:08

Thanks to this other post I found a way to visualize the fill bar in the legend, even though that wasn't what I meant to do.

Here's the ouptup

And the code

df = data.frame(x = c(rnorm(10, mean = 0),
                      rnorm(10, mean = 3)),
                y = c(rnorm(10, mean = 0),
                      rnorm(10, mean = 3)),
                grp = factor(c(rep('a', times = 10),
                               rep('b', times = 10)),
                             levels = c('a', 'b')),
                val = rep(1:10, times = 2)) %>%
  group_by(grp) %>%
  mutate(scaledVal = rescale(val)) %>%
  ungroup %>%
  mutate(scaledValOffSet = scaledVal + 100*(as.integer(grp) - 1))

scalerange <- range(df$scaledVal)
gradientends <- scalerange + rep(c(0,100,200), each=2)

ggplot(data = df,
       aes(x = x,
           y = y)) +
  geom_point(pch = 21,
             aes(fill = scaledValOffSet,
                 size = val)) + 
  scale_fill_gradientn(colours = c('white',
                                   'darkred',
                                   'white',
                                   'deepskyblue4'),
                       values = rescale(gradientends))

Basically one should rescale fill values (e.g. between 0 and 1) and separate them using another order of magnitude, provided by the categorical variable grp. This is not what I wanted though: the snippet can be improved, of course, to make the whole thing less manual, but still lacks the simple usual discrete fill legend.

Mix color and fill aesthetics in ggplot

2 Answers2