R pass variable column indices to ggplot2

Question

I'm attempting to pass the column indices to ggplot as part of a function I'll be using repeatedly. like:

myplot <- function(df){
    ggplot(df, aes(df[, 1], df[, 2])) + geom_point()
}

I'll always be using the first column as my x variable and the second column as my y-variable, but the column names change between data sets. I've searched all over.. Any ideas?

EDIT:

This is the answer I used:

require(ggplot2)

myplot <- function(df){
   ggplot(df, aes_string(colnames(df)[1], colnames(df)[2])) + geom_point()
}

Solution

You can use the aes_string in stead of aes to pass string in stead of using objects, i.e.:

myplot = function(df, x_string, y_string) {
   ggplot(df, aes_string(x = x_string, y = y_string)) + geom_point()
 }
myplot(df, "A", "B")
myplot(df, "B", "A")

Comments

[N8TRO]

Thanks, it works, though not ideal because I'd have to manually give the column names. Any way to get around this?

[baptiste]

aes_string(colnames(df)[1], colnames(df)[2])

[Paul Hiemstra]

In general, in ggplot2 you do not provide vectors in aes. In aes you provide a mapping of the aesthetics of the plot to columns in the data, with no need to hardcode the data in aes.

[Arun]

If you column name is a-b for example, then this gives the error Error in eval(expr, envir, enclos) : object 'a-b' not found. Using environment = environment() with aes is another fix as linked above under OP's post.

[Paul Hiemstra]

I think there is no way, other than passing vectors, in ggplot2 to make a plot with this kind of column name. I never encountered this, but I follow Hadley's style and always use _ ;).

[Arun]

@PaulHiemstra, I already linked one way of doing this (without using column names at all). If you insist on using column names, then try this instead: set.seed(45); df <- data.frame(x=gl(5,5), y=runif(25)); myplot2 = function(df, col1, col2) { ggplot(df, aes(x = get(names(df)[col1]), y = get(names(df)[col2])), environment = environment()) + geom_point() }. From this it is straightforward to change this function to take column names as arguments.

[Paul Hiemstra]

Nice, thanks for the code Arun.

[vruizext]

just was i was looking for, you saved me a good time, thanks :)

[shadow]

@PaulHiemstra, @Arun: Using aes_q is another way of passing non-standard column names to ggplot. Why I think that's the preferable solution see here.

[Bryan Shalloway]

aes_string() is now soft deprecated. I think current tidyverse practice would be to use .data calls, as I show at my solution on this related post: stackoverflow.com/a/69286410/9059865