How to create a function that will change columns values by name conditional to olher variable in R?

Question

I am trying to create a code that uses the value of another variable to mutate only a few columns. I am putting a reproducible example.

Name <- c("Jon", "Bill", "Maria", "Ben", "Tina")
Age <- c(7, 12, 19, 18, 30)
Age_Kid_17 <- NA
Age_Kid_18 <- NA
Age_Kid_20 <- NA


df <- data.frame(Name, Age,Age_Kid_17,Age_Kid_18,Age_Kid_20)

I want to change the values of the columns based on the value of the column 'Age' and use this value to determine what columns I want to change. The following loop does work, but it takes too long on the case that I am working on.

for(i in 1:nrow(df)){
  age_ <- df[i,'Age']
  
  if(age_>21){
    next
  }
  if(age_<17){
    for (a in 17:20){
    df[i,paste0('Age_Kid_',a)] <- 0
    }
  }else{
    for (a in age_:20){
      df[i,paste0('Age_Kid_',a)] <- 0} 
    }
}

Answer 1

Tom's answer is a good option. You could also do it without pivoting in the following way. Also please note, your loop code creates a column called "Age_Kid_19" that is not present in the input data. Is that intended?

The use of rowwise() here is not strictly necessary, but it will ensure that dplyr handles each row separately, much as your loop code does, if that is relevant to your real data.

library(tidyverse)

df %>% 
  rowwise() %>% 
  mutate(across(starts_with('Age_Kid'), ~ifelse(Age > parse_number(cur_column()), NA, 0)))

  Name    Age Age_Kid_17 Age_Kid_18 Age_Kid_20
  <chr> <dbl>      <dbl>      <dbl>      <dbl>
1 Jon       7          0          0          0
2 Bill     12          0          0          0
3 Maria    19         NA         NA          0
4 Ben      18         NA          0          0
5 Tina     30         NA         NA         NA