Mutate data frame via function in R

Question

Sorry for the basic question, but I could not find an example in this forum to solve this question. I've tried this one and this one .

I want to change / create a new variable in my data.frame via function in R and tidyverse:

Example:

crivo <- function(x) {
  x <<- x %>% 
    mutate(resp_1 = if_else(MEMO_RE01 == 0,"VN","FP")) %>% 
    mutate(resp_2 = if_else(MEMO_RE02 == 1,"VP","FN"))
  }
crivo(memo_re)

My data.frame name is "memo_re" , but I'll use this function to other datasets as well, just by changing the x argument. R is creating a new data.frame named x instead of creating a new variable in "memor_re" (original dataset). In other words, I want to assign a function to do that:

memo_re <- memo_re %>% mutate(resp_1 = if_else(MEMO_RE01 == 0,"VN","FP"))

But I need to change many datasets and because of that, I want to be able to specify which dataset I'll change.

reproducible code

library(tidyverse)
memo_re <- data.frame(MEMO_RE01=rep(c(0,1),100), MEMO_RE02=c(0,1))

crivo <- function(x) {
  x <<- x %>% 
    mutate(resp_1 = if_else(MEMO_RE01 == 0,"VN","FP")) %>% 
    mutate(resp_2 = if_else(MEMO_RE02 == 1,"VP","FN"))
}
crivo(memo_re)

Answer 1

R is doing exactly what you've asked it to do. In your crivo function definition, you've written your function to assign the new data frame you've created called x to the R environment. That's what the <<- operator does. After running your code, use ls() to see what's in your environment, then look at x . You'll see everything is there, just as you've asked it to be, including the correctly mutate x dataframe.

> memo_re <- data.frame(MEMO_RE01=rep(c(0,1),100), MEMO_RE02=c(0,1))
> 
> crivo <- function(x) {
+   x <<- x %>% 
+     mutate(resp_1 = if_else(MEMO_RE01 == 0,"VN","FP")) %>% 
+     mutate(resp_2 = if_else(MEMO_RE02 == 1,"VP","FN"))
+ }
> crivo(memo_re)
> ls()
[1] "crivo"   "memo_re" "x"      
> head(x)
  MEMO_RE01 MEMO_RE02 resp_1 resp_2
1         0         0     VN     FN
2         1         1     FP     VP
3         0         0     VN     FN
4         1         1     FP     VP
5         0         0     VN     FN
6         1         1     FP     VP

Now, if you wanted to have crivo() return something that you could then assign any name you wanted, you should use

crivo <- function(x) {
  x %>% 
    mutate(resp_1 = if_else(MEMO_RE01 == 0,"VN","FP"), 
           resp_2 = if_else(MEMO_RE02 == 1,"VP","FN"))
}

Note that I haven't used the <<- operator anywhere. As a result, the crivo fx will be returning the mutated x dataframe so that you could do

new <- memo_re %>% crivo()

This way, you can pipe anything you want to crivo and assign it to any new variable. Alternatively, if you just wanted to call the function on memo_re , you can do that too:

memo_re <- memo_re %>% crivo()

Note that the "classic" way to write a function is to use return() to specify what you want a fx to return. If you don't use return() (as I haven't above), R will return whatever is in the last line. Here, it's just the mutate dataframe.