ggplot2: Hand over variable to function (nonstadndard eval)

Question

I'm trying to write a function in which a grouping variable gets handed over to a ggplot2 expression.


# sample data
df <- data.frame(x = rep(1:20, 5), y = rnorm(100), 
                 grp1 = c(rep("A", 20), rep("B", 20), rep("C", 20), rep("D", 20), rep("E", 20)),
                 grp2 = c(rep("X", 50), rep("Y", 50)),
                 stringsAsFactors = TRUE)

This works

g <- ggplot(df, aes(x, y, color = grp1)) +
  geom_line()

print(g)

This doesn't work


plot_this <- function(mydf, mygroup) {

  g <- ggplot(mydf, aes(x, y, color = mygroup)) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)
Error in FUN(X[[i]], ...) : object 'grp2' not found

This doesn't work either (inspired by dplyr)

plot_this <- function(mydf, mygroup) {

  mygroup <- enquo(mygroup)

  g <- ggplot(mydf, aes(x, y, color = (!! mygroup))) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)
Error in FUN(X[[i]], ...) : object 'grp2' not found

Try this https://stackoverflow.com/a/58786401/786542 – Tung Nov 24 '19 at 17:25 — Tung, Nov 24 '19 at 17:25

score 0 · Answer 1 · answered Nov 24 '19 at 17:29

0

I was missing tidy eval:

plot_this <- function(mydf, mygroup) {

  mygroup <- enquo(mygroup)

  g <- ggplot(mydf, aes(x, y, color = {{mygroup}})) +
    geom_line()
}

p <- plot_this(df, grp2)
print(p)

answered Nov 24 '19 at 17:29

Timm S.

5,135
6
24
38

ggplot2: Hand over variable to function (nonstadndard eval)

1 Answers1