Using geom_text in a for loop with ggplot2

Question

I want to display a list of text labels on a ggplot graph with the geom_text() function.

The positions of those labels are stored in a list.

When using the code below, only the second label appears.

x <- seq(0, 10, by = 0.1)
y <- sin(x)
df <- data.frame(x, y)
g <- ggplot(data = df, aes(x, y)) + geom_line()

pos.x <- list(5, 6)
pos.y <- list(0, 0.5)

for (i in 1:2) {
  g <- g + geom_text(aes(x = pos.x[[i]], y = pos.y[[i]], label = paste("Test", i)))
}

print(g)

Any idea what is wrong with this code?

score 8 · Answer 1 · answered Mar 31 '16 at 10:26

8

I agree with @user2728808 answer as a good solution, but here is what was wrong with your code.

Removing the aes from your geom_text will solve the problem. aes should be used for mapping variables from the data argument to aesthetics. Using it any differently, either by using $ or supplying single values can give unexpected results.

Code

for (i in 1:2) {
  g <- g + geom_text(x = pos.x[[i]], y = pos.y[[i]], label = paste("Test", i))
}

answered Mar 31 '16 at 10:26

Axeman

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1

This is a nice answer, as it deals specifically with the loop aspect of the question. – user2728808 Mar 31 '16 at 14:32

score 4 · Accepted Answer · answered Mar 31 '16 at 10:20

I'm not exactly sure how geom_text can be used within a for-loop, but you can achieve the desired result by defining the text labels in advance and using annotate instead. See the code below.

library(ggplot2)
x <- seq(0, 10, by = 0.1)
y <- sin(x)
df <- data.frame(x, y)

pos.x <- c(5, 6)
pos.y <- c(0, 0.5)
titles <- paste("Test",1:2)
ggplot(data = df, aes(x, y)) + geom_line() + 
annotate("text", x = pos.x, y = pos.y, label = titles)

Using geom_text in a for loop with ggplot2

2 Answers2

Code