Replace multiple columns in data.table using a vector

Question

I am wondering how I can replace the values in multiple columns simultaneously in a data.table.

Something like the following:

fake_DT <- data.table(iter = 1:5, A = 0, B = 0, C =0)
vec = c(1,2,3)
fake_DT[iter == 1, c("A", "B", "C") := vec]

Thanks!

akrun · Accepted Answer · 2021-06-20 19:09:10Z

4

We can convert the vector to list with as.list as data.frame/data.table/tibble etc are all list with columns as elements and having some additional attributes

fake_DT[iter == 1, c("A", "B", "C") := as.list(vec)]

-ouptut

fake_DT
   iter A B C
1:    1 1 2 3
2:    2 0 0 0
3:    3 0 0 0
4:    4 0 0 0
5:    5 0 0 0

In the data.table syntax`, when we use

dt[, c('col1', 'col2' ) := .(5, 3)]`

the .( is a compact way to specify list(5, 3)

edited Jun 20, 2021 at 19:09

answered Jun 20, 2021 at 19:07

akrun

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1 Comment

plausibly_exogenous Over a year ago

Perfect! Can't believe I didn't try this one. Thank you! I will accept this answer after the waiting period has ended.

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