Use dynamic name for new column/variable in `dplyr`

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I want to use dplyr::mutate() to create multiple new columns in a data frame. The column names and their contents should be dynamically generated.

Example data from iris:

library(dplyr)
iris <- as_tibble(iris)

I’ve created a function to mutate my new columns from the Petal.Width variable:

multipetal <- function(df, n) {
    varname <- paste("petal", n , sep=".")
    df <- mutate(df, varname = Petal.Width * n)  ## problem arises here
    df
}

Now I create a loop to build my columns:

for(i in 2:5) {
    iris <- multipetal(df=iris, n=i)
}

However, since mutate thinks varname is a literal variable name, the loop only creates one new variable (called varname) instead of four (called petal.2 – petal.5).

How can I get mutate() to use my dynamic name as variable name?

10 Answers
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