ggplot: aesthetics from variable string without aes_string

Question

i have a variable v containing a data.frame column name.

I now want to plot it against its index.

Normally, plotting a column against its index is easy:

df <- data.frame(a = c(.4, .5, .2))
ggplot(df, aes(seq_along(a), a)) + geom_point()

But in my case, I can’t figure out what incantations to do:

plot_vs <- function(df, count = 2) {
    vs <- paste0('V', seq_len(count)) # 'V1', 'V2', ...
    for (v in vs) {
        # this won’t work because “v” is a string
        print(ggplot(df, aes(seq_along(v), v)) + geom_point())
        # maybe this? but it also doesn’t work (“object ‘v.s’ not found”)
        v.s <- as.symbol(v)
        print(ggplot(df, aes(seq_along(v.s), v.s)) + geom_point())
        # this doesn’t work because i use seq_along, and seq_along('V1') is 1:
        print(ggplot(df, aes_string(seq_along(v), v)) + geom_point())
    }
}
plot_vs(data.frame(V1 = 4:6, V2 = 7:9, V3 = 10:12))

The "get" function returns the value of an object given its name as a string. ggplot(df, aes(seq_along(get(v)), get(v))) + geom_point() — JohannesNE
– JohannesNE, Commented Jun 3, 2015 at 9:13
@JohannesNE sadly it doesn’t work, just like my second idea (“Error in function ‘get’: object ‘v’ not found”) — flying sheep
– flying sheep, Commented Jun 3, 2015 at 9:19
@flyingsheep could you edit your question and clarify why aes_string does not solve your problem? — Anthony Damico
– Anthony Damico, Commented Jun 3, 2015 at 9:44

shadow · Accepted Answer · 2015-06-03 12:31:01Z

1

Your question title explicitly states that you want to do this without aes_string. Here's how you do it with aes_string: use paste.

plot_vs <- function(df, count = 2) {
  vs <- paste0('V', seq_len(count)) # 'V1', 'V2', ...
  for (v in vs) {
    print(ggplot(df, aes_string(paste("seq_along(", v, ")"), v)) + geom_point())
  }
}

plot_vs(data.frame(V1 = 4:6, V2 =7:9, V3 = 10:12))

answered Jun 3, 2015 at 12:31

shadow

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1 Comment

flying sheep Over a year ago

haha, didn’t know that the arguments of aes_string would be fully parsed as expressions. this is a solution!

Anthony Damico · Accepted Answer · 2015-06-03 11:49:20Z

0

library(ggplot2)
df <- data.frame(a = c(.4, .5, .2))
v <- "a"
df$num<-seq(nrow(df))
ggplot(df, aes_string("num", v)) + geom_point()

answered Jun 3, 2015 at 11:49

Anthony Damico

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2 Comments

flying sheep Over a year ago

sure, this works if the data.frame is small enough and if i want to mutate it.

Anthony Damico Over a year ago

you have it inside your function, so any changes to df will be discarded at the end of the call. yes, it only works if you have enough ram to read the data.frame and also add a column of indices.

flying sheep · Accepted Answer · 2015-06-04 14:10:06Z

0

@shadow’s comment gave the hint to find the solution, namely aes_q:

plot_vs <- function(df, count = 2) {
    vs <- paste0('V', seq_len(count)) # 'V1', 'V2', ...
    for (v in vs) {
        v = as.name(v)
        print(ggplot(df, aes_q(substitute(seq_along(v)), v)) + geom_point())
    }
}
plot_vs(data.frame(V1 = 4:6, V2 = 7:9, V3 = 10:12))

answered Jun 4, 2015 at 14:10

flying sheep

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