Use substrings of column names in across

Question

I have the following tibble:

df <- tibble(
  x = c(5, 5),
  Column_1 = c(0.5, 0.5),
  Column_2 = c(0.75, 0.75))

I would like to create two new columns, which are the product of column x and Column_1 and x and Column_2 respectively. These columns should be named ABC_1 and ABC_2.

I tried the following code:

df <- mutate(df,
  across(starts_with("Column_"),
              function(y) y * x,
              .names = paste0("ABC", gsub("Column_", "", "{.col}"))
        ))

However, this resulted in the following table:

x	Column_1	Column_2	ABCColumn_1	ABCColumn_2
5	0.5	0.75	2.5	3.75
5	0.5	0.75	2.5	3.75

The resulting columns are now named ABCColumn_1 and ABCColumn_2. Somehow creating a substring with gsub did not work. My desired output is:

x	Column_1	Column_2	ABC_1	ABC_2
5	0.5	0.75	2.5	3.75
5	0.5	0.75	2.5	3.75

Any ideas how I can elegantly solve this problem? In reality, the number of columns is variable, so I cannot hardcode 1 and 2 into my script.

EDIT: Sorry, my generic columns names were not well chosen. I chose a different one to show that the old and the new column names should not be related in any way except for the number.

jaechang · Answer 1 · 2022-12-02T08:37:10.163

1

    df <- mutate(df,
                 across(starts_with("Column_"),
                        function(y) y * x,
                        .names = paste0("New", gsub("Column_", "", "{.col}"))
                 ))

edited Dec 02 '22 at 08:37

answered Dec 02 '22 at 08:33

jaechang

29
3

Ritchie Sacramento · Accepted Answer · 2022-12-02T10:22:41.127

The glue strings used in the .names argument of across() evaluate calls so you could do:

library(dplyr)

df %>%
  mutate(across(starts_with("Column"), ~ x * .x, .names = "ABC_{seq_along(.col)}"))

# A tibble: 2 × 5
      x Column_1 Column_2 ABC_1 ABC_2
  <dbl>    <dbl>    <dbl> <dbl> <dbl>
1     5      0.5     0.75   2.5  3.75
2     5      0.5     0.75   2.5  3.75

Or use sub() in the glue string:

df %>%
  mutate(across(starts_with("Column"), ~ x * .x, .names = "{sub('Column', 'ABC', .col)}"))

Use substrings of column names in across

2 Answers2