How to delete multiple columns in data.table?

Question

Is that possible to delete multiple columns by reference using data.table?

None of the following works

library(data.table);
dt <- mtcars %>% setDT

# THESE ARE NOT RUNNABLE
dt[, range := NULL, with = F]
dt[, (range) := NULL, with = F]
dt[, ..range:=NULL]
dt[, ':='(.SD=NULL), .SDcols=range] 
dt[, lapply(.SD, NULL), .SDcols=range] 
dt[, ':='(mget(range)):=NULL]

Can you help?

PS. Eventually, for each of the lines above to I would like to know when it can or when it cannot be used (evidently, they can't be used for deleting a range of columns, but they can be used for selecting , or assigning values to, a range of columns)

What is range. Perhaps range <- c("mpg", "cyl"); > dt[, (range) := NULL]; names(dt) [1] "disp" "hp" "drat" "wt" "qsec" "vs" "am" "gear" "carb" — akrun
– akrun, Commented Dec 8, 2021 at 19:35

Marco_CH · Accepted Answer · 2021-12-09 14:44:57Z

2

Try this:

library(data.table)

dt = data.table(mtcars)

dt[, `:=`(wt=NULL, hp=NULL, disp=NULL, am=NULL, gear=NULL, carb=NULL)]

Output:

> head(dt)
    mpg cyl drat  qsec vs
1: 21.0   6 3.90 16.46  0
2: 21.0   6 3.90 17.02  0
3: 22.8   4 3.85 18.61  1
4: 21.4   6 3.08 19.44  1
5: 18.7   8 3.15 17.02  0
6: 18.1   6 2.76 20.22  1

Or as akrun wrote:

range = c("wt", "hp", "disp", "am", "gear", "carb")
dt[, (range):=NULL]

answered Dec 9, 2021 at 14:44

Marco_CH

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Comments

Dean MacGregor · Accepted Answer · 2021-12-09 22:27:15Z

1

If range is something like 1:3 then you could do...

range<-1:3

DT1[,(names(DT1)[range]):=NULL]

or

set(DT1, j=range, value=NULL)

answered Dec 9, 2021 at 22:27

Dean MacGregor

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tdy · Accepted Answer · 2025-07-16 18:41:53Z

0

I know this is a very old post now, but if range is a vector of column names you'd like to remove, you can do this:

DT<-DT[,.SD,.SDcols=-range]

edited Jul 16 at 18:41

tdy

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answered Jul 16 at 15:02

user13678913

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