pandas.Series.asof
Series.asof(where)-
Return last good (non-NaN) value in Series if value is NaN for requested date.
If there is no good value, NaN is returned.
Parameters: where : date or array of dates Returns: value or NaN Notes
Dates are assumed to be sorted
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Licensed under the 3-clause BSD License.
https://pandas.pydata.org/pandas-docs/version/0.18.1/generated/pandas.Series.asof.html