CODEWITHSUNDEEP
rggplot2histogramgradient
dan
dan

Reputation: 6314

Coloring a geom_histogram by gradient

I'm trying to plot a geom_histogram where the bars are colored by a gradient.

This is what I'm trying to do:

library(ggplot2)
set.seed(1)
df <- data.frame(id=paste("ID",1:1000,sep="."),val=rnorm(1000),stringsAsFactors=F)
ggplot(df,aes_string(x="val",y="..count..+1",fill="val"))+geom_histogram(binwidth=1,pad=TRUE)+scale_y_log10()+scale_fill_gradient2("val",low="darkblue",high="darkred")

But getting: enter image description here

Any idea how to get it colored by the defined gradient?

Upvotes: 8

Views: 3300

Answers (3)

stefan
stefan

Reputation: 125038

Instead of binning manually another option would be to make use of the bins computed by stat_bin by mapping ..x.. (or factor(..x..) in case of a discrete scale) or after_stat(x) on the fill aesthetic.

An issue with computing the bins manually is that we end up with multiple groups per bin for which the count has to be computed (even if the count is zero most of the time) and which get stacked on top of each other in the histogram. Especially, this gets problematic if one would add labels of counts to the histogram as can be seen in this post, because in that case one ends up with multiple labels per bin.

library(ggplot2)

set.seed(1)

df <- data.frame(id = paste("ID", 1:1000, sep = "."), val = rnorm(1000), stringsAsFactors = F)

ggplot(df, aes(x = val, y = ..count.. + 1, fill = ..x..)) +
  geom_histogram(binwidth = .1, pad = TRUE) +
  scale_y_log10() +
  scale_fill_gradient2(name = "val", low = "darkblue", high = "darkred")
#> Warning: Duplicated aesthetics after name standardisation: pad

Upvotes: 0

dan
dan

Reputation: 6314

Just for completeness.

If the colors I'd like to have the gradient on to be manually selected here's what I suggest:

data:

library(ggplot2)
set.seed(1)
df <- data.frame(id=paste("ID",1:1000,sep="."),val=rnorm(1000),stringsAsFactors=F)

colors:

bins <- 10
cols <- c("darkblue","darkred")
colGradient <- colorRampPalette(cols)
cut.cols <- colGradient(bins)
cuts <- cut(df$val,bins)
names(cuts) <- sapply(cuts,function(t) cut.cols[which(as.character(t) == levels(cuts))])

plot:

ggplot(df,aes(val,fill=cut(val,bins))) + 
    geom_histogram(show.legend=FALSE) +
    scale_color_manual(values=cut.cols,labels=levels(cuts)) +
    scale_fill_manual(values=cut.cols,labels=levels(cuts))

enter image description here

Upvotes: 5

Simon Jackson
Simon Jackson

Reputation: 3174

Not sure you can fill by val because each bar of the histogram represents a collection of points.

You can, however, fill by categorical bins using cut. For example:

ggplot(df, aes(val, fill = cut(val, 100))) +
  geom_histogram(show.legend = FALSE)

histogram

Upvotes: 17

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