How to use a variable to specify column name in ggplot

Solution 1:

You can use aes_string:

f <- function( column ) {
    ...
    ggplot( rates.by.groups, aes_string(x="name", y="rate", colour= column,
                                        group=column ) )
}

as long as you pass the column to the function as a string (f("majr") rather than f(majr)). Also note that we changed the other columns, "name" and "rate", to be strings.

If for whatever reason you'd rather not use aes_string, you could change it to (the somewhat more cumbersome):

    ggplot( rates.by.groups, aes(x=name, y=rate, colour= get(column),
                                        group=get(column) ) )

Solution 2:

From the release notes of ggplot2 V3.0.0 :

aes() now supports quasiquotation so that you can use !!, !!!, and :=. This replaces aes_() and aes_string() which are now soft-deprecated (but will remain around for a long time).

The idiomatic way now would be to convert to a symbol the string that the variable contains, using sym()(which is almost the same as base aliases as.name() / as.symbol()), and unquote it using !!

Simulating OP's data we can do :

library(tidyverse)
rates.by.groups <- data.frame(
  name = LETTERS[1:3],
  rate = 1:3,
  mjr = LETTERS[c(4,4,5)],
  gender = c("M","F","F")
)

f <- function(column) {
  column <- sym(column)
  ggplot(rates.by.groups, 
         aes(x = name, 
             y = rate, 
             fill  = !!column, 
             group = !!column)) +
    geom_col()
}

f("gender")
f("mjr")
x <- "gender"
f(x)

If we'd rather feed raw names to the function we can do:

f2 <- function(column) {
  column <- ensym(column)
  ggplot(rates.by.groups, 
         aes(x = name, 
             y = rate, 
             fill  = !!column, 
             group = !!column)) +
    geom_col()
}

It will work with names a.k.a. symbols AND with string literals

f2(gender)
f2(mjr)
f2("gender")
f2("mjr")

As Lionel says about ensym():

it's meant to mimic the syntax of arguments where you can supply both in the LHS, e.g. list(bare = 1, "quoted" = 2)

A note on enquo()

enquo()quotes the expression (not necessarily a symbol) fed to the argument, it doesn't convert a string literal to a symbol as ensym() does so it might be less adapted here, but we can do :

f3 <- function(column) {
  column <- enquo(column)
  ggplot(rates.by.groups, 
         aes(x = name, 
             y = rate, 
             fill  = !!column, 
             group = !!column)) +
    geom_col()
}

f3(gender)
f2(mjr)