CODEWITHSUNDEEP
rdplyrpurrr
Misha
Misha

Reputation: 3126

Set parts of listcolumn to NULL in R

library(tidyverse)
data(mtcars)
mtcars <- rownames_to_column(mtcars,var = "car")
mtcars$id <- c(1:length(mtcars$car))
mtcars$make <- map_chr(mtcars$car,~strsplit(.x," ")[[1]][1])

mt2 <- mtcars %>% select(1:4,id,make) %>% nest(-make,.key = "l")
mt4 <- mt2[1:5,]
mt5 <- mt2[1:5,]

`

Now - I´d like to have the listcolumn for mazda set to NULL.

 mt4[mt4$make=="Mazda","l"]<-NULL

However, comparing mt4$l to mt5$l I find that the "mazda" elements have been removed, but that the other elements have been shifted upward. Could someone explain why this is logical? How can I selectively only NULL a certain element within a listcolumn?

Upvotes: 2

Views: 51

Answers (1)

r2evans
r2evans

Reputation: 160607

Please include non-base packages in your questions. In this case, we need:

library(dplyr)
library(purrr)
library(tidyr)
library(tibble)

(or just library(tidyverse), I believe).

By assigning NULL like that to an element, you are telling R to remove that element from the list, thereby making it shorter. If you want to replace the element with a NULL element, try

mt4[mt4$make=="Mazda","l"] <- list(list(NULL))

instead. (This happens to also work if the conditional mt4$make=="Mazda" were to return multiple matches; obviously not a factor with this example, but good to know.)

Upvotes: 3

Related Questions