R using apply function instead of a loop

Question

Very simple problem I'm trying to solve, just can't seem to figure it out. I want to apply a certain criteria which is in a column to a number of columns.

cols_to_change<-['d','e','f']

for one column, d, i can do this:

df$d[which(df$criteria<df$d)]<-NA

But for the other columns,e,f, I could do a for loop, but I wanted to use an apply function instead. How can I do this?

Does this answer your question? [R Apply() function on specific dataframe columns](https://stackoverflow.com/questions/18503177/r-apply-function-on-specific-dataframe-columns) — Repmat, Jul 30 '20 at 10:51
Take a look at this thread: https://stackoverflow.com/questions/18503177/r-apply-function-on-specific-dataframe-columns I've tagged this questions as a duplicate — Repmat, Jul 30 '20 at 10:51
Please use proper R syntax and provide a complete example including input and expected output. — G. Grothendieck, Jul 30 '20 at 11:10

Ric S · Accepted Answer · 2020-07-30T11:10:12.800

2

Without sample data it is difficult to validate what you are trying to do. Anyways, I think you are looking for something like the following

cols_to_change <- c("d", "e", "f")
df[cols_to_change] <- lapply(df[cols_to_change], function(x) ifelse(df$criteria < x, NA, x))

Note that lapply is a preferred version with respect to apply.

edited Jul 30 '20 at 11:10

answered Jul 30 '20 at 10:57

Ric S

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thanks, this is exactly what i was after. I need to learn how to use this functions, it's quite confusing for me! – simonsays Jul 30 '20 at 12:38
1

Just have a look at the documentation and practice, it's the most efficient way to learn :) – Ric S Jul 30 '20 at 12:49

R using apply function instead of a loop

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