Pivoting dataset to long format for all variable pairs following specific name pattern

Question

I've got data from an experiment with 2 conditions where each participant got tested in both conditions for various properties. The dataset is in wide format, the variable name pattern is like this: variables for condition A start with MM7M, for condition B they start with MMsf7M, then the abbreviation for the property is appended, e.g. MM7Mabc and MMsf7Mabc. I want to reshape the dataset to long format, so each participant gets 2 rows, one for condition A and one for condition B; there should be only one column for the condition, having the values A and B and for each property a column, named after the property, e.g. abc. Because there hundreds of properties, I would like to do the pivoting automatically for all variable pairs that follow the pattern condition+someproperty. Any help much appreciated.

EDIT for clarification: I meant creating a new variable for each property, i.e. abc, abcde, xyz, total_c, so there are only 2 rows for each participant.

library(tidyverse)

data <- tibble(
  id = c(1, 2, 3, 4),
  MM7Mabcde = c(2, 4, 2, 2),
  MMsf7Mabcde = c(4, 6, 3, 4),
  MM7Mxyz = c(2, 4, 4, 2),
  MMsf7Mxyz = c(6, 8, 9, 9),
  MM7Mtotal_c = c(6, 5, 4, 1),
  MMsf7Mtotal_c = c(12, 18, 22, 32),
  someVar = c(5, 6, 9, 9)
)

Answer 1

As long as your condition names have some regular expression in common, you can use names_pattern, with the special name .value in names_to

pivot_longer(data, contains("7M"), 
             names_pattern = "^(.*7M)(.*)$",
             names_to = c("Condition", ".value"))
#> # A tibble: 8 x 6
#>      id someVar Condition abcde   xyz total_c
#>   <dbl>   <dbl> <chr>     <dbl> <dbl>   <dbl>
#> 1     1       5 MM7M          2     2       6
#> 2     1       5 MMsf7M        4     6      12
#> 3     1       6 MM7M          4     4       5
#> 4     1       6 MMsf7M        6     8      18
#> 5     2       9 MM7M          2     4       4
#> 6     2       9 MMsf7M        3     9      22
#> 7     3       9 MM7M          2     2       1
#> 8     3       9 MMsf7M        4     9      32