Update a ggplot using a for loop (R) [duplicate]

Question

I am having some problems updating a ggplot object. What I want to do is to put a vertical line in a specific location that I change on every loop, hence: multiple lines will be displayed in different locations. However, when I use a for loop it only shows me the last line that it's created but when I do it manually it works. I created a reproductible example that you guys can check:

library(ggplot2)

x <- ggplot(mapping = aes(x = 1:100, y = 1:100)) +
  geom_line()

for(i in 1:6){
  x <- x + geom_vline(aes(xintercept = i*5))
}

y <- ggplot(mapping = aes(x = 1:100, y = 1:100)) +
  geom_line()

y <- y + geom_vline(aes(xintercept = 5))
y <- y + geom_vline(aes(xintercept = 10))
y <- y + geom_vline(aes(xintercept = 15))
y <- y + geom_vline(aes(xintercept = 20))
y <- y + geom_vline(aes(xintercept = 25))
y <- y + geom_vline(aes(xintercept = 30))

Check both plots. Why is the first plot not looking the same as the second one, although for me both processes do the "same" thing?

Using aes_ instead of aes in the geom_vline for-loop will give you the same plot as y. — Adam Quek
– Adam Quek, Commented Jun 2, 2017 at 2:49

Fustincho · Accepted Answer · 2017-09-25 14:51:26Z

8

I was looking at some contributions that some people left me and there is one who solves it pretty efficiently and it is to use aes_() instead of aes(). The difference is that aes_() forces to evaluate and update the plot, while aes() only evaluates the indexes when the plot is drawn. Hence: it never updates while it is inside a for loop.

library(ggplot2)

x <- ggplot(mapping = aes(x = 1:100, y = 1:100)) +
  geom_line()

for(i in 1:6){
  x <- x + geom_vline(aes_(xintercept = i*5))
}

edited Sep 25, 2017 at 14:51

answered Jun 1, 2017 at 22:19

Fustincho

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1 Comment

pep Over a year ago

This is a very simple solution to the problem with lazy evaluation in looping.

Alex Gold · Accepted Answer · 2017-06-01 21:49:33Z

0

It has to do with how ggplot does lazy evaluation -- see here.

Since geom_vline is vectorized, this works:

library(ggplot2)

x <- ggplot() +
  geom_line(mapping = aes(x = 1:100, y = 1:100))

x + geom_vline(aes(xintercept = seq(5,30,5)))

answered Jun 1, 2017 at 21:49

Alex Gold

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1 Comment

Fustincho Over a year ago

Thanks for the help, Alex. Actually, your example works in this reproductible example but it is quite limited in other applications. I was just reading some other comments that people let me and the best solution is to use aes_() instead of aes().

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