Usage of ggplot2 inside R function

Question

I want to write an R function that reads in a file m, and plots a boxplot using ggplots2.

This is function:

stringplotter = function(m, n) {
library(ggplot2)
require(scales)
data<-as.data.frame(read.table(file=m, header=T, dec=".", sep="\t"))
ggplot(data, aes(x=string, y=n)) + geom_boxplot() + geom_point() + scale_y_continuous(labels=comma)
}

An example file test:

C   string
97  ccc
95.2    ccc
88.6    nnn
0.5 aaa
86.4    nnn
0   ccc
85  nnn
73.9    nnn
87.9    ccc
71.7    nnn
94  aaa
76.6    ccc
44.4    ccc
92  aaa
91.2    ccc

When I then call the function

stringplotter("test", C)

I get the error

Fehler: Column `y` must be a 1d atomic vector or a list
Call `rlang::last_error()` to see a backtrace

When I call the commands inside the function directly, everything works as expected. Where is my error?

See this article tidyverse.org/articles/2018/07/ggplot2-tidy-evaluation — Jack Brookes
– Jack Brookes, Commented Dec 9, 2018 at 15:28

Indrajeet Patil · Accepted Answer · 2018-12-09 15:32:35Z

2

The problem is that when you write y = n, ggplot2 doesn't know how to evaluate value of n. You can use rlang to quote the input and it will be evaluated within the entered dataframe-

stringplotter <- function(m, n) {
  library(ggplot2)
  require(scales)
  data <-
    as.data.frame(read.table(
      file = m,
      header = T,
      dec = ".",
      sep = "\t"
    ))
  ggplot(data, aes(x = string, y = !!rlang::enquo(n))) + 
    geom_boxplot() + 
    geom_point() + 
    scale_y_continuous(labels = comma)
}

answered Dec 9, 2018 at 15:32

Indrajeet Patil

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