Dplyr: filter() discards rownames

[kforner]

Hello,

filter() does discard rownames, e.g.:

rownames(filter(mtcars, cyl == 4))
[1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11"
rownames(mtcars[mtcars$cyl == 4, ])
[1] "Datsun 710" "Merc 240D" "Merc 230" "Fiat 128"
[5] "Honda Civic" "Toyota Corolla" "Toyota Corona" "Fiat X1-9"
[9] "Porsche 914-2" "Lotus Europa" "Volvo 142E"

Is it on purpose, a limitation or planned ?
I could not find any explanation in the documentation.

Thanks
Karl

[hadley]

Yes, all dplyr methods ignore rownames.

[kforner]

Thanks, but that does not completely answer the question: is-it on purpose, or something you may consider adding ?

[hadley]

On purpose. They're hard to get right in general (esp because of uniqueness criterion) and don't allow you to do anything that you can't otherwise do.

[James-Arnold]

Sometimes there is useful information in the rownames however. Arguably it should already be part of the data, but how about adding a draw_rownames function as a short cut for people to do this?
Something like:

draw_rownames <- function(.data) .data %>% do(mutate(.,rownames=rownames(.)))

mtcars %>% draw_rownames() %>% filter(carb==6)
   mpg cyl disp  hp drat   wt qsec vs am gear carb     rownames
1 19.7   6  145 175 3.62 2.77 15.5  0  1    5    6 Ferrari Dino

[ronammar]

Is it possible to include a flag to instruct dplyr functions to include rownames?

[hadley]

No, sorry.

[liyun831229]

keep row names is really important

[dnehar]

Use subset() instead ...