How to create conditional error bars in ggplot

Question

I am trying to display conditional error bars, for example, when I ran this I see the error bars for all values.

d <- qplot(cyl, mpg, data=mtcars)
d + stat_summary(fun.ymin=min,fun.ymax=max,geom="errorbar")

I would like to display the above error bars only if N > than a specified value. Is there a way of doing this?

teunbrand · Accepted Answer · 2020-05-05 23:51:26Z

2

Sure, you could build function factories for the fun.ymin and fun.ymax arguments that only give the value if the input length exceeds some number. The only downside is though that it has to return some value, so you'll get a warning about that.


library(ggplot2)

nmax <- function(n) {
  n <- force(n)
  function(x) {
    if (length(x) >= n) {
      max(x)
    } else {
      NA_real_
    }
  }
}

nmin <- function(n) {
  n <- force(n)
  function(x) {
    if (length(x) >= n) {
      min(x)
    } else {
      NA_real_
    }
  }
}

d <- qplot(cyl, mpg, data=mtcars)
d + stat_summary(fun.ymin = nmin(8), fun.ymax = nmax(8), geom = "errorbar")
#> Warning: Removed 1 rows containing missing values (geom_errorbar).

^{Created on 2020-05-06 by the reprex package (v0.3.0)}

If you find that specifying N two times is too cumbersome / error prone, you can also make regular functions that take n as an argument and pass fun.args:

nmax2 <- function(x, n) {
  if (length(x) >= n) {
    max(x)
  } else {
    NA_real_
  }
}

nmin2 <- function(x, n) {
  if (length(x) >= n) {
    min(x)
  } else {
    NA_real_
  }
}

d <- qplot(cyl, mpg, data=mtcars)
d + stat_summary(fun.ymin = nmin2, fun.ymax = nmax2, fun.args = list(n = 8), geom = "errorbar")

edited May 5, 2020 at 23:51

answered May 5, 2020 at 23:46

teunbrand

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3 Comments

Axeman Over a year ago

Alternatively, pass a subset of the data to stat_summary using the data argument. For example use data = . %>% group_by(cyl) %>% filter(n() >= 8)

Jeni Over a year ago

@Axeman Hi! I am trying to use this solution. However, instead of passing a fixed argument to my functions I would like to pass the value of the dots that I am plotting. This is my code:

ggplot(data=chr1, aes(x=x_values0, y=AF))+ geom_point(aes(col=color), size=2)+ stat_summary(aes(fun.ymin = ymin(AF, sdPopHetAF), fun.ymax = ymax(AF, sdPopHetAF)), geom = "errorbar")

AF and sdPopHetAF are variables from chr, the dataframe indicated in the beginning. However, it is not detecting this variables and not working. How can I solve this?

Axeman Over a year ago

@Jeni, it's better if you ask a new question, and show a reproducible example of your problem. I don't see anything obviously wrong, other than your code has chr1 as data, but you say your data is chr.

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