mutate or summarise across rows by variable containing string

Question

I'd like to create a new data table which is the sum across rows from variables which contain a string. I have been trying to keep this within the tidyverse as a noob using new dplyr across. Help much appreciated.

dat<- data.frame("Image" = c(1,2,3,4), 
                 "A" = c(1,2,3,4),
                 "A:B"= c(5,6,7,8),
                 "A:B:C"= c(9,10,11,12))

to obtain the sums across the rows of variables containing "A", "B", or "C".

datsums<- data.frame("Image" = c(1,2,3,4),
                     "Asum"= c(15,18,21,24),
                     "Bsum"=c(14,16,18,20),
                     "Csum"=c(9,10,11,12))

I have been unsuccessful using the newer dplyr verbs:

datsums<- dat %>% summarise(across(str_detect("A")), sum, .names ="Asum",
across(str_detect("B")), sum, .names="Bsum",
across(str_detect("C")), sum, .names"Csum")

Answer 1

use rowwise and c_across:

library(tidyverse)

dat %>% 
  rowwise() %>% 
  summarise(
    Asum = sum(c_across(contains("A"))),
    Bsum = sum(c_across(contains("B"))),
    Csum = sum(c_across(contains("C")))
  )

Returns:

`summarise()` ungrouping output (override with `.groups` argument)
# A tibble: 4 x 3
   Asum  Bsum  Csum
  <dbl> <dbl> <dbl>
1    16    14     9
2    20    16    10
3    24    18    11
4    28    20    12

---

To add columns to the original data.frame, use mutate instead of summarise:

dat %>% 
  rowwise() %>% 
  mutate(
    Asum = sum(c_across(contains("A"))),
    Bsum = sum(c_across(contains("B"))),
    Csum = sum(c_across(contains("C")))
  )

# A tibble: 4 x 7
# Rowwise: 
  Image     A   A.B A.B.C  Asum  Bsum  Csum
  <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
1     1     1     5     9    16    14     9
2     2     2     6    10    20    16    10
3     3     3     7    11    24    18    11
4     4     4     8    12    28    20    12