Pandas.datetimeindex.snap Timestamps To Left Occurring Frequency

I would like to have the same functionality that snap but using the left occurring frequency instead of the nearest. This is what I am trying: date = pd.date_range('2015-01-01',

Solution 1:

I find the solution in pandas snap source code:

use rollback instead:

from pandas.tseries.frequencies import to_offset  
freq = to_offset('W-MON')  
date.map(freq.rollback)