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BUG: Set frequency for empty Series #14458

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BUG: Set frequency for empty Series #14458

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4 changes: 4 additions & 0 deletions doc/source/whatsnew/v0.20.0.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -598,6 +598,10 @@ Bug Fixes


- Bug in the display of ``.info()`` where a qualifier (+) would always be displayed with a ``MultiIndex`` that contains only non-strings (:issue:`15245`)

- Bug in ``DataFrame.loc`` with indexing a ``MultiIndex`` with a ``Series`` indexer (:issue:`14730`)
- Bug in ``asfreq``, where frequency wasn't set for empty Series (:issue:`14320`)

- Bug in ``pd.read_msgpack()`` in which ``Series`` categoricals were being improperly processed (:issue:`14901`)
- Bug in ``Series.ffill()`` with mixed dtypes containing tz-aware datetimes. (:issue:`14956`)

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8 changes: 8 additions & 0 deletions pandas/tests/frame/test_timeseries.py
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Expand Up @@ -398,6 +398,14 @@ def test_asfreq_fillvalue(self):
actual_series = ts.asfreq(freq='1S', fill_value=9.0)
assert_series_equal(expected_series, actual_series)

def test_asfreq_datetimeindex_empty_series(self):
# GH 14340
expected = Series(index=pd.DatetimeIndex(
["2016-09-29 11:00"])).asfreq('H')
result = Series(index=pd.DatetimeIndex(["2016-09-29 11:00"]),
data=[3]).asfreq('H')
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Can you create one of the two without using asfreq.

Further, it is not fully clear what is what you actually testing, as the result of the empty series is called expected (you typically call the constructed expected value expected to compare the result of what you want to test)

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@jorisvandenbossche Actually the issue was that we didn't set frequency properly for empty series. Hence I'm testing this particular thing by comparing with frequency of a non-empty Series that we make using similar parameters with an empty one.

self.assert_index_equal(expected.index, result.index)

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compare the series, e.g. assert_series_equal, and construct the expected directly.

you have two results to compare here, what you currently have labeled as expected and as result.

make another tests where you construct the expected directly (iow, dont' use .asfreq) . IOW you actually should use a direc

def test_first_last_valid(self):
N = len(self.frame.index)
mat = randn(N)
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5 changes: 4 additions & 1 deletion pandas/tseries/resample.py
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Expand Up @@ -1388,7 +1388,10 @@ def asfreq(obj, freq, method=None, how=None, normalize=False, fill_value=None):
return new_obj
else:
if len(obj.index) == 0:
return obj.copy()
new_index = obj.index._shallow_copy(freq=to_offset(freq))
new_obj = obj.copy()
new_obj.index = new_index
return new_obj
dti = date_range(obj.index[0], obj.index[-1], freq=freq)
dti.name = obj.index.name
rs = obj.reindex(dti, method=method, fill_value=fill_value)
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