Removing rows by reference using data.table?

Question

I am trying to figure out how to remove a group of rows from a dataset by reference. For example, with this data set:

testset <- data.table(date=as.Date(c("2013-07-02","2013-08-03","2013-09-04","2013-10-05","2013-11-06")), 
           yr = c(2013,2013,2013,2013,2013), 
           mo = c(07,08,09,10,11), 
           da = c(02,03,04,05,06), 
           plant = LETTERS[1:5], 
           product = as.factor(letters[26:22]), 
           rating = runif(25))

I want to remove all rows where the product is "y". I have no idea how to go about this.

[This is on the to-do list](http://r-forge.r-project.org/tracker/index.php?func=detail&aid=2092&group_id=240&atid=978). — Arun, Apr 11 '14 at 04:14
@Arun I can't seem to access the above link (I see a "Permission Denied" message on R-Forge). Has this feature been implemented? — random_forest_fanatic, Dec 24 '14 at 19:49
@random_forest_fanatic, oops, we have moved to github. Here is the new link: [FR #635](https://github.com/Rdatatable/data.table/issues/635). Sorry we have not gotten to it yet. — Arun, Dec 24 '14 at 20:23

score -4 · Accepted Answer · answered Apr 11 '14 at 11:08

-4

you can use either of the following commands -

testset_new <- subset(testset,product!="y")

or

testset_new <- testset[testset$product!="y",]

answered Apr 11 '14 at 11:08

RHelp

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This doesn't answer the question since it copies the data.table. – Roland Apr 11 '14 at 12:58
In that case, you overwrite your existing data - testset <- subset(testset,product!="y") – RHelp Apr 15 '14 at 09:47
@RHelp That's not the point. What if you are inside the function and you are expected to modify the data.table given in the arguments? Replacing **is not** modification in place (by reference). – Adam Ryczkowski Jul 01 '16 at 22:39

Removing rows by reference using data.table?

1 Answers1