FR: auto-infer LHS of := when absent

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by reading the tstrsplit entry point and the existing := and set assignment behavior. Reproduce the ragged-column example from the issue, then determine how an assign argument should infer destination names and preserve the original table. Done means split results are added as extra columns without losing x, y, or z.

Written by the indexing model from the issue text.

Description

top request

It's something of a nuisance to assign ragged columns with tstrsplit, if we don't necessarily know how many columns will result ex ante. Is it possible to add an assign argument which would use := or set to add the result as extra columns to the table?

DT <- data.table(x = c("a/b/c/d", "a/b/c", "a/b"),
                 y = 1:3, z = 4:6)
DT[ , tstrsplit(x, "/")]
#    V1 V2 V3 V4 #`x`, `y`, and `z` are irrecoverable
#1:  a  b  c NA
#2:  a  b NA NA
#3:  a  b  c  d

Workaround (ugly)

DT[ , paste0("V", 1:max(sapply(spl <- strsplit(x, "/"), length))) := transpose(spl)][]
#          x y z V1 V2 V3 V4
#1:   a/b/c 1 5  a  b  c NA
#2:     a/b 2 6  a  b NA NA
#3: a/b/c/d 3 7  a  b  c  d

Inspired by this SO question

Dominant language
R
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