How do I treat an element of a list as a column of dataframe for loop

March 17, 2023

I am trying to treat the values in a list as column names to filter against in a for loop using R. However, R seems to be treating the values as strings, not actual column names. For example, let’s say that I have a dataframe with 3 columns: PERSON_NAME, SCORE_1 and SCORE_2. Then I store the "SCORE_1" and "SCORE_2" as values within as list. I want to write a for loop that creates two data frames, one with students who scored >90 on the first exam and another with >90 on the second exam.

The following does it without a for loop.

library(dplyr)

# Create a dataframe of test scores
df <- data.frame(
  PERSON_NAME = c('JIM', 'SALLY', 'JOHN', 'SUE'),
  SCORE_1 = c(100, 95, 80, 85),
  SCORE_2 = c(95, 75, 90, 97)
)

# Find students with SCORE_1 greater than 90
df %>%
  filter(
    SCORE_1 > 90
  ) %>%
  select(
    PERSON_NAME,
    SCORE_1
  )

# Find students with SCORE_2 greater than 90
df %>%
  filter(
    SCORE_2 > 90
  ) %>%
  select(
    PERSON_NAME,
    SCORE_2
  )

When I try a for loop, it doesn’t seem to work. I get two data frames with the right columns, however, the filtering is not working. How do I adjust the below to make the filter step work? Thank you!

for (i in 1:length(list_of_tests)) {
  x <- df %>%
    filter(
      list_of_tests[i] > 90
    ) %>%
    select(
      PERSON_NAME,
      list_of_tests[i]
    )
  
  assign(list_of_tests[i],x)
}

>Solution :

Using tidyverse

library(purrr)
library(dplyr)
 map(threshold_cols, ~ df %>%
   filter(if_any(all_of(.x), ~ .x > 90)))

-output

$SCORE_1
  PERSON_NAME SCORE_1 SCORE_2
1         JIM     100      95
2       SALLY      95      75

$SCORE_2
  PERSON_NAME SCORE_1 SCORE_2
1         JIM     100      95
2         SUE      85      97