rbindlist edge case inconsistency

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by reproducing Cases I–III with the rbindlist entry point in the issue. Compare the handling of NULL elements and the warning behavior; done means Case I retains its column and fills the missing value with NA consistently with Cases II and III.

Written by the indexing model from the issue text.

Description

[rbind|cbind|merge]list consistency

Consider the difference in behavior here:

# --- CASE I : one empty item, one column, one populated ---
(l = list(list(NULL), list(1L)))
# [[1]]
# [[1]][[1]]
# NULL

# [[2]]
# [[2]][[1]]
# [1] 1
rbindlist(l)
#    V1
# 1:  1

# --- CASE II : One item, two columns, one empty ---
(l = list(list(NULL, 1L)))
# [[1]]
# [[1]][[1]]
# NULL

# [[1]][[2]]
# [1] 1
#    V1 V2
# 1: NA  1

# --- CASE III : Two items, two columns, one each empty ---
(l = list(list(NULL, 1L), list(1L, NULL)))
# [[1]]
# [[1]][[1]]
# NULL

# [[1]][[2]]
# [1] 1

# [[2]]
# [[2]][[1]]
# [1] 1

# [[2]][[2]]
# NULL
rbindlist(l)
#    V1 V2
# 1: NA  1
# 2:  1 NA

Given Cases II and III, I would expect Case I to also fill the NULL value with NA (with the same warning), rather than to eliminate it altogether.

Dominant language
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