eval doesn't work on join columns
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Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 45/100
Research direction
Start by running the two data.table expressions from the issue and compare their evaluation scope: the chained form returns 5, while the join form cannot find b. Trace how eval receives join columns and verify that the join form produces the same result as the working expression.
Written by the indexing model from the issue text.
Description
dt1 = data.table(a = 1, key = 'a')
dt2 = data.table(a = 1, b = list(quote(5*a)), key = 'a')
#this works:
dt1[dt2][, eval(b[[1]], .SD)]
#[1] 5
# this doesn't (but should produce exact same result as above)
dt1[dt2, eval(b[[1]], .SD)]
#Error in eval(b[[1]], .SD) : object 'b' not found
Relevant SO post - http://stackoverflow.com/a/30899285/817778
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