passing string to ggplot function

Question

I would like to have a function that i could apply to any object that meets a criteria, and have a nice ggplot scatter plot with regression line print.

However, i cannot generalise what i can do at the REPL with code.

so i have this working:

require(ggplot2)    
require(xts)
set.seed(1)
dd = xts(cbind(rnorm(10), runif(10)), order.by = Sys.Date() + 1:10)
names(dd) <- c('d1', 'd2')

gp <- ggplot(data = dd, 
             aes(x = d1, y = d2)) + 
        geom_point(shape=1) + 
        geom_smooth(method = lm)

But this fails

PointReg <- function(Xts, a=1, b=2) {
    stopifnot(is.xts(Xts), 
              ncol(Xts) >1)
    tempData <- Xts[, c(a,b)]
    gPlot <- ggplot(data = tempData, 
                aes(x = colnames(tempData)[1],
                   y = colnames(tempData)[2])) +
            geom_point(shape=1) +
            geom_smooth(method = lm)
    gPlot
}

What am i doing wrong?

Andrie · Accepted Answer · 2013-11-26 08:00:35Z

2

Your function throws an error since aes() tries to evaluate the argument in the column names of your data. To be more specific, aes() tries to evaluate colnames(tempData)[1] as a column name and this column doesn't exist.

To fix this, you somehow have to tell ggplot that you are not passing a column name, but an expression (a string) that will resolve to a column name.

Use aes_string() for this. Concretely, simply replace aes() with aes_string(). Try this:

PointReg <- function(Xts, a=1, b=2) {
  stopifnot(is.xts(Xts), 
            ncol(Xts) >1)
  tempData <- Xts[, c(a,b)]
  gPlot <- ggplot(data = tempData, 
                  aes_string(x = colnames(tempData)[1],
                      y = colnames(tempData)[2])) +
    geom_point(shape=1) +
    geom_smooth(method = lm)
  gPlot
}

enter image description here

answered Nov 26, 2013 at 8:00

Andrie

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Raffael · Accepted Answer · 2013-11-26 07:35:03Z

2

You can specify the columns using indexes.

> library(ggplot2)
> df <- data.frame(a = 1:10, b = 1:10, c=c("x"))
> ggplot(data = df, aes(x = df[,1], y = df[,2])) + geom_line()

answered Nov 26, 2013 at 7:35

Raffael

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Mirabilis · Accepted Answer · 2023-06-27 19:25:02Z

1

Since aes_string is now deprecated, the way to use strings within ggplot is to use !!ensym():

d1 <- "d1"
d2 <- "d2"
ggplot(data, aes(x= !!ensym(d1), y= !!ensym(d2))) + geom_line()

Source: How does enquote/quote/!! works in ggplot

answered Jun 27, 2023 at 19:25

Mirabilis

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