R: check multiple variables using 'for' loop and 'case_when.'

Question

I have a dataset DT as below:
category: number 1-9
xxx, yyy, zzz: binary (0,1)

category xxx yyy zzz
8         1   0   0
1         0   0   0
4         0   1   1
9         0   0   1
8         0   1   0

I would like to check multiple conditions using 'for' loop and 'case_when.'
So, I wish the data shows at the end

category xxx yyy zzz result_xxx result_yyy result_zzz
8         1   0   0       8           0          0
1         0   0   0       0           0          0
4         0   1   1       0           4          4 
9         0   0   1       0           0          9 
8         0   1   0       0           8          0

To do it, I wrote a code below:

condition.vars <- c("xxx", "yyy", "zzz")

for(i in condition.vars){
  browser()
  DT <- DT[, condition:= case_when(
    ([[i]] == 1 & category ==1) ~ 1,
    ([[i]] == 1 & category ==2) ~ 2,
    ([[i]] == 1 & category ==3) ~ 3,
    ([[i]] == 1 & category ==4) ~ 4,
    ([[i]] == 1 & category ==5) ~ 5,
    ([[i]] == 1 & category ==6) ~ 6,
    ([[i]] == 1 & category ==7) ~ 7,
    ([[i]] == 1 & category ==8) ~ 8,
    ([[i]] == 1 & category ==9) ~ 9,
    TRUE ~ 0
  )]
  setnames(DT, "condition", paste0("result", i))
   
} 

And as you expect, it does not work.
Would you please help me to correct my code?

Answer 1

You don't need a for loop or case_when. If you have a dataframe you can simplify this as :

condition.vars <- c("xxx", "yyy", "zzz")
DT[paste0('result_', condition.vars)] <- DT$category * DT[condition.vars]

#  category xxx yyy zzz result_xxx result_yyy result_zzz
#1        8   1   0   0          8          0          0
#2        1   0   0   0          0          0          0
#3        4   0   1   1          0          4          4
#4        9   0   0   1          0          0          9
#5        8   0   1   0          0          8          0

If DT is data.table you can do :

library(data.table)
DT[, paste0('result_', condition.vars):= category * .SD,.SDcols = condition.vars]