How to convert dataframe column names from strings into arguments suitable for (qplot, ggplot2)?

Question

I want to write a function that takes a dataframe, and graphs all the columns in that dataframe as histograms.

For a dataframe whose column names I know beforehand, I can write

qplot(colname1, data=df, geom='histogram')
qplot(colname2, data=df, geom='histogram')
...

but I want to do this generically, so that I can use the name of the column as a string "colname1".

In other words, how to write

plot_histogram_of_column <- function(df, colname) {
    # qplot(colname, data=df, geom='histogram') won't work
}

joran · Accepted Answer · 2014-09-26 15:36:00Z

19

Use ggplot and aes_string. Something like this:

ggplot(data = df, aes_string(x = colname)) + geom_histogram()

aes_string was written precisely for this purpose.

edited Sep 26, 2014 at 15:36

answered Dec 20, 2011 at 4:42

joran

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4 Comments

Maxy-B Over a year ago

As documented here: had.co.nz/ggplot2/aes.html Note, though, that, as far as I can tell, NO page of the ggplot2 documentation site links to this, so the only way to find it is by knowing to search for it.

joran Over a year ago

@Maxy-B The built-in docs (?aes) are much improved in version 0.9.0, and contain a link to the help page for aes_string. I can't recall if this was the case in 8.9.0.

smci Over a year ago

Yes. I just independently solved my own problem related to this. This function is incredibly obscure and hard to discover, yet important. Surely one of the first things you would want to parameterize when plotting a large dataset is the identity of the y-series, yet the examples don't emphasisize this. (I edited your title for clarity)

moodymudskipper Over a year ago

The idiomatic way is now : ggplot(data = df, aes(x = !!ensym(colname))) + geom_histogram()

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