I would like to create a new column containing plotmath expressions that I later plan to use somewhere else in the analysis pipeline.
Here is a minimal example along with I tried. For example, here I am trying to create a new column called label that will have a different plotmath expression depending on the value of y column.
This doesn't seem to work:
# loading needed libraries
library(tidyverse)
# creating a dataframe
df <- data.frame(x = c(1:10), y = c(rep("a", 5), rep("b", 5))) %>%
tibble::as_data_frame(x = .)
# adding a new column with plotmath expression
df %>%
dplyr::mutate(.data = .,
label = dplyr::case_when(
y == "a" ~ paste(list(
"'This is'", "~alpha==", 1
), sep = ""),
y == "b" ~ paste(list(
"'This is'", "~beta==", 2
), sep = "")))
#> Error in mutate_impl(.data, dots): Evaluation error: `y == "a" ~ paste(list("'This is'", "~alpha==", 1), sep = "")`, `y == "b" ~ paste(list("'This is'", "~beta==", 2), sep = "")` must be length 10 or one, not 3.
Created on 2018-06-26 by the reprex package (v0.2.0).
The error message is showing that each case is returning length 3. This is because when you paste() a list using sep, you'll get a vector of the same length as the list, so
paste(list(
"'This is'", "~alpha==", 1
), sep = "")
returns a vector of length 3, not 1 or 10 as required. If instead, you use the collapse argument of paste(), you'll get a vector of length 1. In context:
df %>%
dplyr::mutate(.data = .,
label = dplyr::case_when(
y == "a" ~ paste(list(
"'This is'", "~alpha==", 1
), collapse = ""),
y == "b" ~ paste(list(
"'This is'", "~beta==", 2
), collapse = "")))
# A tibble: 10 x 3
# x y label
# <int> <fct> <chr>
# 1 1 a 'This is'~alpha==1
# 2 2 a 'This is'~alpha==1
# 3 3 a 'This is'~alpha==1
# 4 4 a 'This is'~alpha==1
# 5 5 a 'This is'~alpha==1
# 6 6 b 'This is'~beta==2
# 7 7 b 'This is'~beta==2
# 8 8 b 'This is'~beta==2
# 9 9 b 'This is'~beta==2
#10 10 b 'This is'~beta==2