how to compare two grouper 'freq' windows-CodePudding

Function foo first summarizes values in given dataframe by p1 and then by p2, where p1 and p2 are offset aliases.

import pandas as pd
import numpy as np

# Function
def foo(d, p1, p2, brk):
    # assert p2 > p1
    s1 = df.groupby(pd.Grouper(freq=p1)).sum().gt(brk)
    s2 = s1.groupby(pd.Grouper(freq=p2)).sum()
    return s2

# Data
df = pd.DataFrame({"datetime": pd.date_range("2017-01-01", "2017-03-31", freq="1H")})
np.random.seed(42)
df["val"] = np.random.sample(2137)
df = df.set_index("datetime")

foo(df, "7D", "1M", 80)
#             val
# datetime       
# 2017-01-31    4
# 2017-02-28    3
# 2017-03-31    3

The goal is to implement assert p2 > p1 so that the result of foo is meaningful. One way would be to convert both p1 and p2 to Timedelta and compare them. However, some aliases such as 1M aren't valid for conversion to Timedelta.

pandas.Timedelta("1M") gives following warning:

FutureWarning: Units 'M', 'Y' and 'y' do not represent unambiguous timedelta values and will be removed in a future version

pd.Grouper(freq="1M") > pd.Grouper(freq="7D") gives following error:

TypeError: '>' not supported between instances of 'TimeGrouper' and 'TimeGrouper'

What is the proper way to compare two grouper freq windows?

CodePudding user response：

Based on this answer, you could probably do something like this:

def foo(d, p1, p2, brk):
    from pandas.tseries.frequencies import to_offset
    from datetime import datetime
    tmp = datetime.now()
    assert tmp   to_offset(p2) > tmp   to_offset(p1), 'p1 must be less than p2'
    
    s1 = d.groupby(pd.Grouper(freq=p1)).sum().gt(brk)
    s2 = s1.groupby(pd.Grouper(freq=p2)).sum()
    return s2

Test:

>>> foo(df, "7D", "1M", 80)
---------------------------------------------------------------------------
AssertionError                            Traceback (most recent call last)
Input In [51], in <cell line: 1>()
----> 1 foo(df, "7D", "1M", 80)

Input In [50], in foo(d, p1, p2, brk)
      3 from datetime import datetime
      4 tmp = datetime.now()
----> 5 assert tmp   to_offset(p1) > tmp   to_offset(p2), 'p1 must be less than p2'
      7 s1 = d.groupby(pd.Grouper(freq=p1)).sum().gt(brk)
      8 s2 = s1.groupby(pd.Grouper(freq=p2)).sum()

AssertionError: p1 must be less than p2