Creating new columns in for loop data.table

Question

I want to create new columns in for loop.

impute.sum <- function(x) replace(x, is.na(x), -sum(x, na.rm = TRUE))
df = data.table(user = c(1,1,2,2,3,3,3), x1 = c(NA, 2, 4, NA, NA, 1, 1), x2 = c(1, NA, NA, 3, 4, NA, NA))
df[, x1_1 := impute.sum(x1), by = user]
df[, x2_1 := impute.sum(x2), by = user]

I don't know exactly how many columns I will have, so I need to do it with for loop.

Have you seen the reference semantics vignette?

Arun
– Arun

2016-03-02 10:21:57 +00:00
Commented Mar 2, 2016 at 10:21 — Arun
– Arun, Commented Mar 2, 2016 at 10:21
Thanks, @Arun. I've found the answer.

Vitaliy Radchenko
– Vitaliy Radchenko

2016-03-02 10:27:56 +00:00
Commented Mar 2, 2016 at 10:27 — Vitaliy Radchenko
– Vitaliy Radchenko, Commented Mar 2, 2016 at 10:27

Vitaliy Radchenko · Accepted Answer · 2016-03-02 11:57:24Z

2

There is the answer even without using for loop

impute.sum <- function(x) replace(x, is.na(x), -sum(x, na.rm = TRUE))
df = data.table(user = c(1,1,2,2,3,3,3), x1 = c(NA, 2, 4, NA, NA, 1, 1), x2 = c(1, NA, NA, 3, 4, NA, NA))
in_cols  = c("x1", "x2")
out_cols = c("x1_1", "x2_1")
df[, c(out_cols) := lapply(.SD, impute.sum), by = user, .SDcols = in_cols]

edited Mar 2, 2016 at 11:57

answered Mar 2, 2016 at 10:26

Vitaliy Radchenko

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