NULL in mutate

[hadley]

Should remove variable, e.g.:

mtcars %>% mutate(cyl = NULL)

[romainfrancois]

I pushed the basics for that. Couple questions though:

• what happens if the variable was not in the dataset. Right now, nothing happens. Should this be an error.
• what happens if we attempt to rm a grouping variable ?Now we get:

> mtcars %>% group_by(cyl) %>% mutate(cyl = NULL)
Erreur : cannot modify grouping variable

We inherit behavior for when we modify the variable. Should we instead get a new message, e.g. "cannot remove grouping variable"

[hadley]

I think both of those are fine.

[romainfrancois]

Alright. Closing this then.