r - Plot every column in a data frame as a histogram on one page using ggplot

Question

I would like to plot each column of a data.frame using a histogram on one page. Here is an example using the sample "diamonds" data set which comes with R:

p = list()
for (i in 1:ncol(diamonds)) p[[i]] <- qplot(diamonds[,i], xlab=names(diamonds)[[i]])
do.call(grid.arrange, p)

This does plot all the columns, but the data looks the same in each one. So, something is clearly wrong.

Is this the right approach for this task? I'm sure I have some silly syntax somewhere that is assigning the same column data set to each element in the list, but I'm not sure what it is.

Thank you

Answer 1

Here you go:

library(reshape2)
library(ggplot2)
d <- melt(diamonds[,-c(2:4)])
ggplot(d,aes(x = value)) + 
    facet_wrap(~variable,scales = "free_x") + 
    geom_histogram()

melting allows us to use the resulting grouping variables (called variable) to split the data into groups and plot a histogram for each one. Note the use of scales = "free_x" because each of the variables has a markedly different range and scale.