head(0) and tail(0) return empty DataFrames by trvrm · Pull Request #11937 · pandas-dev/pandas (original) (raw)
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closes #11930
frame.head(0) and frame.tail(0) now return empty DataFrames.
| return self |
|---|
| if n == 0: |
| return self.iloc[l:] |
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I think self.iloc[0:0] is clearer here. I don't think you need l anymore (was it ever needed?).
The side question here is: should we check that n>0? I don't think we need to... as this will make it kinda useful: it'll return the rest of the dataframe except the head(n) == tail(len(df) - n).
Edit: or n>=0.
make sure to test groupby! (need updating maybe)
Fixing the broken unit test....
| @@ -2146,8 +2147,10 @@ def tail(self, n=5): |
|---|
| Returns last n rows |
| """ |
| l = len(self) |
| if l == 0 or n == 0: |
| if l == 0: |
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This l is not required. self.iloc[-0:] == self :)
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So why was it there in the first place? I don't really understand what its doing in either head() or tail().
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I think it was due to the n == 0 or n == l check that was there before. Even in that case there's no need to avoid the iloc in the latter case; code is simpler without it.
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Ok, I've taken the checks out.
I don't really understand why Travis is failing - it seems to be some kind of connection error? Is that something I've done wrong?
Looks unrelated. squash and maybe the tests will pass next time :)
I'm sorry, I'm not sure what you mean by 'squash'.
Ah, ok. I think I did that right, hopefully the tests will pass this time.
Need more thing, a release note in doc/source/whatsnew/v0.18.0, maybe under the API changes section, to document the change. You can squash that commit as well (which you did correctly). Thanks!
Added a note in the release docs.
| @@ -166,6 +166,7 @@ Backwards incompatible API changes |
|---|
| - The parameter ``out`` has been removed from the ``Series.round()`` method. (:issue:`11763`) |
| - ``DataFrame.round()`` leaves non-numeric columns unchanged in its return, rather than raises. (:issue:`11885`) |
| - ``DataFrame.head(0)`` and ``DataFrame.tail(0)`` return empty frames, rather than ``self``. (:issue:`11937`) |
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Mention Series as well here
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done
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actually Series was already doing this. But that's fine.
unit test for Series.head(0), Series.tail(0)
fixed breaking unit tests on Series.head(0)/Series.tail(0)
removed unnecessary length checks
added documentation
mention series in API docs
ok, lgtm. ping when green.
hayd added a commit that referenced this pull request
head(0) and tail(0) return empty DataFrames