Using dplyr in assignment

Asked Oct 13 '15 at 19:01

Active Oct 13 '15 at 19:13

Viewed 585 times

I have a question about dplyr.

Lets say I want to update certain values in a dataframe, can I do this?:

mtcars %>% filter(mpg>20) %>% select(hp)=1000

(The example is nonsensical where all cars with MPGs greater than 20 have HP set to 1000)

I get an error so I am guessing the answer is no I can't use %>% and the dplyr verbs to the left of an assignment, but the dplyr syntax is a lot cleaner than:

mtcars[mtcars$mpg>20,"hp"]=1000

Especially when you are dealing with more complex cases, so I wanted to ask if there is any way to use the dplyr syntax in this case?

edit: It looks like mutate is the verb I want, so now my question is, can I dynamically change the name of the var in the mutate statement like so:

for (i in c("hp","wt")) {mtcars<-mtcars %>% filter(mpg>20) %>% mutate(i=1000) }

This example just creates a column named "i" with value 1000, which isn't what I want.

edited Oct 13 '15 at 19:13

asked Oct 13 '15 at 19:01

Carl

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Do you want `mtcars %>% mutate(hp = ifelse(mpg>20, 1000, hp))`? – jeremycg Oct 13 '15 at 19:04
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mutate(mtcars,hp=ifelse(mpg>20,1000,hp) – scoa Oct 13 '15 at 19:06
Thanks, that did the trick – Carl Oct 13 '15 at 19:08
In vanilla R, you can do things like `x[ y > 20 ] <- 1000`, but dplyr doesn't support it. If you're interested in trying yet another package, this is doable in data.table: `DT <- data.table(mtcars); DT[mpg > 20, hp := 1000]` – Frank Oct 13 '15 at 19:09
Can I change the name of the new var in the mutate statement dynamically? – Carl Oct 13 '15 at 19:14
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I think this might answer that question: http://stackoverflow.com/q/26003574/1191259 – Frank Oct 13 '15 at 19:16

Using dplyr in assignment

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