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Ensure decoding as datetime64[ns] #59

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Merged
merged 2 commits into from
Mar 12, 2014
Merged

Ensure decoding as datetime64[ns] #59

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5a90275
Ensure decoding as datetime64[ns]
shoyer Mar 10, 2014
931db24
Fix encoding for datetime64[ns]
shoyer Mar 10, 2014
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13 changes: 7 additions & 6 deletions src/xray/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -137,7 +137,8 @@ def decode_cf_datetime(num_dates, units, calendar=None):
or max_date > datetime(2262, 4, 11)):
dates = nc4.num2date(num_dates, units, calendar)
else:
# we can safely use np.datetime64
# we can safely use np.datetime64 with nanosecond precision (pandas
# likes ns precision so it can directly make DatetimeIndex objects)
if min_num == max_num:
# we can't safely divide by max_num - min_num
dates = np.repeat(np.datetime64(min_date), num_dates.size)
Expand All @@ -158,8 +159,8 @@ def decode_cf_datetime(num_dates, units, calendar=None):
denominator = max_num - min_num
dates = (time_delta * numerator / denominator
+ np.datetime64(min_date))
# restore original shape
dates = dates.reshape(num_dates.shape)
# restore original shape and ensure dates are given in ns
dates = dates.reshape(num_dates.shape).astype('M8[ns]')
return dates


Expand Down Expand Up @@ -203,11 +204,11 @@ def encode_cf_datetime(dates, units=None, calendar=None):
and np.issubdtype(dates.dtype, np.datetime64)):
# for now, don't bother doing any trickery like decode_cf_datetime to
# convert dates to numbers faster
# TODO: don't use pandas.DatetimeIndex to do the conversion
dates = pd.Index(dates.reshape(-1)).to_pydatetime().reshape(dates.shape)
# note: numpy's broken datetime conversion only works for us precision
dates = np.asarray(dates).astype('M8[us]').astype(datetime)

if hasattr(dates, 'ndim') and dates.ndim == 0:
# date2num doesn't like 0-dimensional arguments
# unpack dates because date2num doesn't like 0-dimensional arguments
dates = dates.item()

num = nc4.date2num(dates, units, calendar)
Expand Down
12 changes: 11 additions & 1 deletion test/test_utils.py
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Expand Up @@ -89,7 +89,17 @@ def test_cf_datetime(self):
for calendar in ['standard', 'gregorian', 'proleptic_gregorian']:
expected = nc4.num2date(num_dates, units, calendar)
actual = utils.decode_cf_datetime(num_dates, units, calendar)
self.assertArrayEqual(expected, actual)
if (isinstance(actual, np.ndarray)
and np.issubdtype(actual.dtype, np.datetime64)):
self.assertEqual(actual.dtype, np.dtype('M8[ns]'))
# For some reason, numpy 1.8 does not compare ns precision
# datetime64 arrays as equal to arrays of datetime objects,
# but it works for us precision. Thus, convert to us
# precision for the actual array equal comparison...
actual_cmp = actual.astype('M8[us]')
else:
actual_cmp = actual
self.assertArrayEqual(expected, actual_cmp)
encoded, _, _ = utils.encode_cf_datetime(actual, units, calendar)
self.assertArrayEqual(num_dates, np.around(encoded))
if (hasattr(num_dates, 'ndim') and num_dates.ndim == 1
Expand Down