# A Quick Appreciation of the R transform Function

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`R`

users who also use the `dplyr`

package will be able to quickly understand the following code that adds an estimated area column to a `data.frame`

.

suppressPackageStartupMessages(library("dplyr")) iris %>% mutate( ., Petal.Area = (pi/4)*Petal.Width*Petal.Length) %>% head(.)

## Sepal.Length Sepal.Width Petal.Length Petal.Width Species Petal.Area ## 1 5.1 3.5 1.4 0.2 setosa 0.2199115 ## 2 4.9 3.0 1.4 0.2 setosa 0.2199115 ## 3 4.7 3.2 1.3 0.2 setosa 0.2042035 ## 4 4.6 3.1 1.5 0.2 setosa 0.2356194 ## 5 5.0 3.6 1.4 0.2 setosa 0.2199115 ## 6 5.4 3.9 1.7 0.4 setosa 0.5340708

The notation we used above is the “explicit argument” variation we recommend for readability. What a lot of `dplyr`

users do not seem to know is: base-`R`

already has this functionality. The function is called `transform()`

.

To demonstrate this, let’s first detach `dplyr`

to show that we are not using functions from `dplyr`

.

detach("package:dplyr", unload = TRUE)

Now let’s write the equivalent pipeline using exclusively base-`R`

.

iris ->. transform( ., Petal.Area = (pi/4)*Petal.Width*Petal.Length) ->. head(.)

## Sepal.Length Sepal.Width Petal.Length Petal.Width Species Petal.Area ## 1 5.1 3.5 1.4 0.2 setosa 0.2199115 ## 2 4.9 3.0 1.4 0.2 setosa 0.2199115 ## 3 4.7 3.2 1.3 0.2 setosa 0.2042035 ## 4 4.6 3.1 1.5 0.2 setosa 0.2356194 ## 5 5.0 3.6 1.4 0.2 setosa 0.2199115 ## 6 5.4 3.9 1.7 0.4 setosa 0.5340708

The “`->.`

” notation is a the end-of-line variation of the Bizarro Pipe. The `transform()`

function has been part of `R`

since 1998. `dplyr::mutate()`

was introduced in 2014.

git log --all -p --reverse --source -S 'transform <-' commit 41c2f7338c45dbf9eac99c210206bc3657bca98a refs/remotes/origin/tags/R-0-62-4 Author: pd <[email protected]> Date: Wed Feb 11 18:31:12 1998 +0000 Added the frametools functions subset() and transform() git-svn-id: https://svn.r-project.org/R/[email protected] 00db46b3-68df-0310-9c12-caf00c1e9a41

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