weird exception when by contains get

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Assessment

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

Research direction

No source file or test is named. Start by running the supplied data.table example and compare the filtered and unfiltered grouping expressions; done means the filtered expression no longer raises the “object 'z' not found” error and produces the expected grouped result.

Written by the indexing model from the issue text.

Description

programming

Just copied my question on stackoverflow:

get function usually works without problems in data.table, but I am not able to understand the reason of this bug.

library(data.table)
tb<-data.table(x=c(1,2), y=c(3,4), z=c(5,6), w=c("a","b"))
tb[w != "b", .(x=sum(x)), by=.(y, zz=z)] #OK
#    y zz x
# 1: 3  5 1
tb[, .(x=sum(x)), by=.(y, zz=get("z"))] #OK
#    y zz x
# 1: 3  5 1
# 2: 4  6 2
tb[w != "b", .(x=sum(x)), by=.(y, zz=get("z"))] #not OK?!

Error in get("z") : object 'z' not found

(I use R version 3.3.2 and data.table version 1.9.6.)

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