How can I overlay histograms previously created with ggplot2?

Question

I need to create different histograms from a dataframe. Currently I am using this loop to generate individual histograms

An example:

df<-matrix(NA,2000,5) df[,1]<-rnorm(2000,1,1) df[,2]<-rnorm(2000,2,1) df[,3]<-rnorm(2000,3,1) df[,4]<-rnorm(2000,4,1) df[,5]<-rnorm(2000,5,1) df<-data.frame(df) colnames(df) <- c("HB1", "HB2", "HB3","HB4", 'HB5')

Loop:

out<-list() for (i in 1:5){ x = df[,i] out[[i]] <- ggplot(data.frame(x), aes(x)) + geom_histogram(aes(y=..count../sum(..count..)), fill="red", lwd=0.9, breaks=seq(0,5,0.1), col=("black"), alpha=I(.9)) + labs(x=expression(d["HB"]), y="Frequency") grid.arrange(out[[i]], ncol=1) }

The output are 5 figures like this one:

But now I would like to do a comparison overlapping all of them. This figure is what I really want:

Thanks in advance

Richard Telford · Accepted Answer · 2016-07-05 23:17:03Z

Reshape the data with tidyr::gather then use the fill aesthetic and 'position = "identity"'

df2 <- tidyr::gather(df) head(df2) # key value #1 HB1 0.7493090 #2 HB1 2.5475796 #3 HB1 0.7756661 #4 HB1 1.2562534 #5 HB1 0.2757356 #6 HB1 2.4831947 ggplot(df2, aes(x = value, fill = key)) + geom_histogram(aes(y=..count../sum(..count..)), breaks=seq(0,5,0.1), alpha=.6, position = "identity") + labs(x=expression(d["HB"]), y="Frequency")

To try a density plot instead, which as eipi10 points out might be easier to understand, use

ggplot(df2, aes(x = value, fill = key)) + geom_density(alpha=.6) + labs(x=expression(d["HB"]), y="Frequency")

Probably much easier to understand as a density plot, rather than a histogram.

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