Mutated data.tables are not printed when enclosed in parentheses.

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Reproduce the two examples from the issue, comparing explicit print(dt[, a := "a"]) with the parenthesized expression (dt[, a := "a"]). Start by tracing how the data.table := mutation is evaluated and displayed in each case. Done means the parenthesized mutation prints the resulting table consistently with the explicit print call.

Written by the indexing model from the issue text.

Description

print

The walrus operator suppresses printing, but calling print explicitly does work.

library(data.table)
dt <- data.table(x = 1)

print(dt[, a := "a"])
#>        x      a
#>    <num> <char>
#> 1:     1      a

However, I woudl've assumed that enclosing the expression in parentheses would also work. It doesn't!

(dt[, a := "a"])

Created on 2025-10-05 with reprex v2.1.1

Dominant language
R
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