python pandas timedelta specific rows

Question

I have a dataframe of a season's worth of basketball scores and I would like to find the number of days between games for each team for every game they have played in the season.

Example frame:

  testDateFrame = pd.DataFrame({'HomeTeam': ['HOU', 'CHI', 'DAL', 'HOU'],
                          'AwayTeam' : ['CHI', 'DAL', 'CHI', 'DAL'],
                          'HomeGameNum': [1, 2, 2, 2],
                          'AwayGameNum' : [1, 1, 3, 3],
                          'Date' : [datetime.date(2014,3,11), datetime.date(2014,3,12),     datetime.date(2014,3,14), datetime.date(2014,3,15)]})

My desired output is this:

  AwayGameNum AwayTeam Date  HomeGameNum HomeTeam AwayRest  HomeRest
        1      CHI  2014-03-11    1      HOU        nan       nan
        1      DAL  2014-03-12    2      CHI        nan        0
        3      CHI  2014-03-14    2      DAL         1         1
        3      DAL  2014-03-15    2      HOU         0         3 

Where the AwayRest, HomeRest columns are the number of days between games for the AwayTeam, HomeTeam -1

Answer 1

I would adjust your data layout a bit so that it fits with Hadley Wickhams' definition of Tidy Data. This make the calculation much simpler. Eliminate the columns for AwayTeam and HomeTeam, and make a single column with Team. Then crate a boolean column (HomeTeam) for whether the team is the home team.

Note: I didn't change the AwayGameNum and HomeGameNum, so the numbers won't match your desired output. But the method will work.

In [34]: df
Out[34]: 
   AwayGameNum Team       Date  HomeGameNum HomeTeam
0            1  CHI 2014-03-11            1    False
1            1  HOU 2014-03-11            1     True
2            1  DAL 2014-03-12            2    False
3            1  CHI 2014-03-12            2     True
4            3  CHI 2014-03-14            2    False
5            3  DAL 2014-03-14            2     True
6            3  DAL 2014-03-15            2    False
7            3  HOU 2014-03-15            2     True

[8 rows x 5 columns]

In [62]: rest = df.groupby(['Team'])['Date'].diff() - datetime.timedelta(1)

In [63]: df['HomeRest'] = rest[df.HomeTeam]

In [64]: df['AwayRest'] = rest[~df.HomeTeam]

In [65]: df
Out[65]: 
   AwayGameNum Team       Date  HomeGameNum HomeTeam  HomeRest  AwayRest
0            1  CHI 2014-03-11            1    False       NaT       NaT
1            1  HOU 2014-03-11            1     True       NaT       NaT
2            1  DAL 2014-03-12            2    False       NaT       NaT
3            1  CHI 2014-03-12            2     True    0 days       NaT
4            3  CHI 2014-03-14            2    False       NaT    1 days
5            3  DAL 2014-03-14            2     True    1 days       NaT
6            3  DAL 2014-03-15            2    False       NaT    0 days
7            3  HOU 2014-03-15            2     True    3 days       NaT

[8 rows x 7 columns]