How subtract two columns correlativelly in a data frame

Context

We would like to know how subtract columns, two by two. Specifically, we want to subtract the columns of the dataframe as follow:

the u_2018 - u_2019.
the u_2019 - u_2020.
the u_2020 - u_2021.
the u_2021 - u_2022.

We looked for a optimal solution in the several stackoverflow question posts, like this (How to subtract two columns using tidyverse mutate with columns named by external variables), but the only undesired approach achieved is datiled in the R code used section. The R session version is 4.2.0 and the dplyr package version is 1.0.9.

Input data in R session

> dat
# A tibble: 6 × 5
          u_2018        u_2019        u_2020        u_2021        u_2022
           <int>         <int>         <int>         <int>         <int>
 1         90035         88015         76135         50725         16517
 2            20            NA            NA         13792         12793
 3           555           620         15032         19309          6479
 4         11171         11782         10281          8974          3901
 5            NA        116896         40169         13191          3610

R code used


dat %>%
  mutate(
    diff_2018_2019 = u_2018 - u_2019,
    diff_2019_2020 = u_2019 - u_2020,
    diff_2020_2021 = u_2020 - u_2021,
    diff_2021_2022 = u_2021 - u_2022)

Question

We would like to know the optimal solution to subtract two by two columns. Maybe one approach includes mutate_at() or across to obtain the differences between and save the subtraction in new columns.

Thanks in advance

Solution

You could use pmap_dfr + diff:

library(purrr)

pmap_dfr(df, ~ -diff(c(...))) %>%
  set_names(~ as.integer(sub('u_', '', .x)) %>% paste('dif', . - 1, ., sep = '_'))

# # A tibble: 5 × 4
#   dif_2018_2019 dif_2019_2020 dif_2020_2021 dif_2021_2022
#           <int>         <int>         <int>         <int>
# 1          2020         11880         25410         34208
# 2            NA            NA            NA           999
# 3           -65        -14412         -4277         12830
# 4          -611          1501          1307          5073
# 5            NA         76727         26978          9581

Note that diff() defaults to subtract the former from the latter, so you need to invert the sign with -diff().

Data

df <- structure(list(u_2018 = c(90035L, 20L, 555L, 11171L, NA), u_2019 = c(88015L, 
NA, 620L, 11782L, 116896L), u_2020 = c(76135L, NA, 15032L, 10281L, 40169L),
u_2021 = c(50725L, 13792L, 19309L, 8974L, 13191L), u_2022 = c(16517L, 
12793L, 6479L, 3901L, 3610L)), class = "data.frame", row.names = c("1", "2", "3", "4", "5"))