How to change values based on if another column contains specific text?

January 4, 2022

I have a dataset where I need to change values for any device that does not contain the text "INV" to 0.

    
Device     Value
RGM        4279
INV A1     727
INV A2     3731
POA        73974

I figured something like this would work, but it doesn’t.

if (grepl(!"INV", df$Device, fixed = TRUE) {
  df$Value <- 0
}

Any ideas?

>Solution :

Base Solution

To modify things the way you originally intended, simply subscript df$Value to target the nonmatches, and overwrite then with <- 0:

df$Value[!grepl("INV", df$Device, fixed = TRUE)] <- 0

Tidy Alternative

Alternatively, if you want to work within tidyverse convention, this should do the trick with dplyr:

library(dplyr)

df <- df %>%
  # Mutate the column as a whole.
  mutate(
    Value = if_else(
      # Determine which values in the column do NOT (!) match the regex.
      !grepl("INV", Value, fixed = TRUE),
      # Overwrite any matches with 0; otherwise keep the original value.
      0, Value
    )
  )