Calculating specific columns across rows

[Bee_2]

I feel like this is a very simple question, I just can't figure it out. I have a dataset with about 60 rows and 40 columns. I would like to take a few columns and sum them according to each row to create a new column. What is the command for this?

[williaml]

Can you provide a reproducible example?

Otherwise, something like this using mtcars to get the sum for all of the columns that contain an 'a' in the name.

library(dplyr)
mtcars |> 
  rowwise() |> 
  mutate(test = sum(across(contains("a")))) |> 
  ungroup()

test = drat + am + gear + carb

# A tibble: 32 x 12
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb  test
   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
 1  21       6  160    110  3.9   2.62  16.5     0     1     4     4 12.9 
 2  21       6  160    110  3.9   2.88  17.0     0     1     4     4 12.9 
 3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1  9.85
 4  21.4     6  258    110  3.08  3.22  19.4     1     0     3     1  7.08
 5  18.7     8  360    175  3.15  3.44  17.0     0     0     3     2  8.15
 6  18.1     6  225    105  2.76  3.46  20.2     1     0     3     1  6.76
 7  14.3     8  360    245  3.21  3.57  15.8     0     0     3     4 10.2 
 8  24.4     4  147.    62  3.69  3.19  20       1     0     4     2  9.69
 9  22.8     4  141.    95  3.92  3.15  22.9     1     0     4     2  9.92
10  19.2     6  168.   123  3.92  3.44  18.3     1     0     4     4 11.9 
# i 22 more rows
# i Use `print(n = ...)` to see more rows