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first called on zero length input #309

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jangorecki opened this issue Sep 13, 2019 · 1 comment
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first called on zero length input #309

jangorecki opened this issue Sep 13, 2019 · 1 comment
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@joshuaulrich
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bug
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0.12-0

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@jangorecki
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We have just recently spotted this inconsistency (with relation to last function) in data.table. It was now amended. It looks to be the same in xts.

A = numeric()
xts::first(A)
#[1] NA
xts::last(A)
#numeric(0)

IMO it make sense to return numeric(0) from first(numeric()).
xts 0.11.2
@jangorecki jangorecki mentioned this issue Sep 13, 2019
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@joshuaulrich
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Hi Jan, thanks for the report! I agree that both first() and last() should return numeric(0). That is consistent with head() and tail(). I will fix.

@joshuaulrich joshuaulrich self-assigned this Nov 19, 2019
@joshuaulrich joshuaulrich added this to the 0.12-0 milestone Nov 19, 2019
joshuaulrich added a commit that referenced this issue Nov 19, 2019
@joshuaulrich
Return zero-row matrix if input is zero-row
d27ab89 
The default methods for first() and last() should return a zero-row
matrix if the input is a zero-length matrix. This makes them (almost)
consistent with head() and tail() in the utils package. (The only
difference is that utils::tail.matrix() adds rownames by default, and
last.default() will not.)

Also update the tests for vector inputs to check the output matches
the input, not the output of head()/tail(). This will avoid potential
test failures in the unlikely event that head()/tail() change in the
future.

See #309.
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