Apply a function to a specific column for every row in a dataframe in R

Question

I want to apply a user defined function to a specific column for every row in a dataframe in R and save the result back into the column.

stroz · Accepted Answer · 2017-02-28 06:31:59Z

6

After nearly 3 hours of reading Stack Overflow answers about slightly different use cases and playing around with apply, lapply, sapply etc. here's the code that allows you to do this:

your_function <- function(x) {
    if(x == 3) {
        x = 333
    } else {
        x = 1
    }
}

df$colname <- sapply(df$colname, your_function)

answered Feb 28, 2017 at 6:31

stroz

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4 Comments

umutto Over a year ago

Did you know the answer before asking it?

Saurabh Chauhan Over a year ago

Why question and answer both are posted in the same time? If you know the answer than what is the reason for posting the question?

stroz Over a year ago

Well, seeing as I couldn't find the answer to my question elsewhere. I figured perhaps posting what I found might help someone else with the same question. There's actually a checkbox you can check to answer your own question.

Hobo Over a year ago

Yeah, it's explicitly encouraged: stackoverflow.com/help/self-answer Thanks for sharing @stroz - it helped me

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