r - How to use a variable to specify column name in ggplot

Question

I have a ggplot command

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

inside a function. But I would like to be able to use a parameter of the function to pick out the column to use as colour and group. I.e. I would like something like this

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

So that the column used in the ggplot is determined by the parameter. E.g. for f("majr") we get the effect of

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

but for f("gender") we get the effect of

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

Some things I tried:

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

did not work. Nor did

e <- environment() 
ggplot( rates.by.groups, aes(x=name, y=rate, colour= columnName , group=columnName ), environment=e )

Answer 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) ) )