Selecting data frame columns to plot in ggplot2

Question

I have a big table of data with ~150 columns. I need to make a series of histograms out of about 1/3rd of them. Rather than putting 50 lines of the same plot command in my script, I want to loop over a list telling me which columns to use. Here is a test dataset to illustrate:

d <- data.frame(c(rep("A",5), rep("B",5)),
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE))

colnames(d) <- c("col1","col2","col3","col4","col5","col6" )


ggplot(data=d, aes(col2, fill= col1)) + geom_density(alpha = 0.5)

So, rather than writing this a 50 times and replacing the aes() values, I really want to do something more like this...

cols_to_plot <- c("col2","col4","col6")

for (i in length(cols_to_plot)) {
  ggplot(data=d, aes(cols_to_plot[i], fill= col1)) + geom_density(alpha = 0.5)

}

But of course, this doesn't work... Is there a way to do this kind of thing?

Thanks!

possible duplicate of How to convert dataframe column names from strings into arguments suitable for (qplot, ggplot2)? — mnel
– mnel, Commented Nov 6, 2012 at 22:50

Harlan · Accepted Answer · 2012-11-06 22:50:45Z

10

I think you'd be better off if you melted your data. Try this:

library(reshape2)
d2 <- melt(d, id='col1')
ggplot(d2, aes(value, fill=col1)) + geom_density(alpha=.5) + facet_wrap(~variable)

Or, if you wanted to do what you originally wanted, use aes_string, like:

ggplot(data=d, aes_string(cols_to_plot[i], fill='col1')) + geom_density(alpha = 0.5)

answered Nov 6, 2012 at 22:50

Harlan

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1 Comment

Herman Toothrot Over a year ago

I am still not sure how to plot only certain columns without using a loop, it should be possible with ggplot, no?

Gavin Simpson · Accepted Answer · 2023-02-16 14:26:12Z

8

Since version 3.0.0 of ggplot2, the aes_string() function has been soft deprecated, with the focus now to use aes().

The trick now is to use the .data object to refer to the data object supplied to ggplot(), which here is d.

Using this, we recover the behviour prior to version 3.0.0 without the soft deprecation wraning:

d <- data.frame(c(rep("A",5), rep("B",5)),
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE))

colnames(d) <- c("col1","col2","col3","col4","col5","col6" )

cols_to_plot <- c("col2","col4","col6")

for (i in seq_along(cols_to_plot)) {
  print(ggplot(data = d,
               aes(x = .data[[cols_to_plot[i]]], fill= .data[["col1"]])) +
    geom_density(alpha = 0.5))
}

Original answer using `aes_string()`

There is an alternative to aes(); aes_string(). With this you can pass in strings for the aesthetic mappings. Note you have to quote col1 here in fill = "col1". Also note that in a for() loop you need to explicitly print() a ggplot object in order for the plot to be drawn on the current device.

d <- data.frame(c(rep("A",5), rep("B",5)),
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE),     
                sample(c(1:10), 10, replace=TRUE))

colnames(d) <- c("col1","col2","col3","col4","col5","col6" )

cols_to_plot <- c("col2","col4","col6")

for (i in seq_along(cols_to_plot)) {
  print(ggplot(data=d, aes_string(x = cols_to_plot[i], fill= "col1")) +
    geom_density(alpha = 0.5))
}

edited Feb 16, 2023 at 14:26

answered Nov 6, 2012 at 22:52

Gavin Simpson

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2 Comments

caddymob Over a year ago

Indeed, this would have had me on a wild goose chase for sure!

BestGirl Over a year ago

For the record: "aes_string() was deprecated in ggplot2 3.0.0. Please use tidy evaluation ideoms [sic] with aes()".

mnel · Accepted Answer · 2012-11-06 22:55:31Z

4

Yes, aes_string

cols_to_plot <- c("col2","col4","col6")

for (i in cols_to_plot) {
  ggplot(data=d, aes_string(i, fill= 'col1')) + geom_density(alpha = 0.5)

}

edited Nov 6, 2012 at 22:55

answered Nov 6, 2012 at 22:49

mnel

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Comments

metasequoia · Accepted Answer · 2012-11-06 22:54:02Z

3

lapply() could be used here in place of a for loop with aes_string().

cols_to_plot <- c("col2","col4","col6")
lapply(cols_to_plot,function(i){
  ggplot(data=d, aes_string(x=i, fill= 'col1')) + 
    geom_density(alpha = 0.5)
} )

answered Nov 6, 2012 at 22:54

metasequoia

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