Group the dataframe based on ids and stick the values of ids to each other with mean of the last days

Admin 1
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I have a data frame, I want to group the data based on the ids and then stick the values for each id together. However, since the number of the ids are not equal, I have to fill the missing values for those ids with same values of the day before.

I have provided an example as below, for example, for id=1, id=2 there is two dates, but for id=3, there are three days.

df = pd.DataFrame()
df['id'] = [1, 1, 2,2, 3, 3, 3]
df['date'] = ['2019-01-01', '2019-01-03', '2019-01-01','2019-01-02', '2019-01-01',   '2019-01-02','2019-01-03']
df['val1']  = [10, 100, 20, 30, 40, 50, 60]
df['val2']  = [30, 30, -20, -30, -40,-50, -60 ]
df['val3']  = [50, 10, 120, 300, 140, 150, 160]

I have tried with the following code:

DF_sticked            = df.filter(regex='val\d+', axis=1).groupby(df['id'])\
                         .apply(np.ravel).apply(pd.Series).rename(lambda x: f"val{x}", axis=1).reset_index().fillna(0)

But, in the above code, I fill the missing value with 0. And also the missing value are at the end of the columns. The output that I want is as follow. As you can see, the val 4, val5, val 6 of id=1 is same as the values of the day before. or the val 7, 8, 9 of id=2 is equal to the the day before.

   val0  val1   val2  val3  val4   val5   val6  val7   val8
id                                                          
1   10.0  30.0   50.0  10.0  30.0   50.0  100.0  30.0   10.0
2   20.0 -20.0  120.0  30.0 -30.0  300.0   30.0 -30.0  300.0
3   40.0 -40.0  140.0  50.0 -50.0  150.0   60.0 -60.0  160.0

Thank you so much.

pandas dataframe python
2 Answers

You can actually pivot the dataframe, then then groupy the dates, transform('mean'), and ffill:

tmp = df.pivot(index='id', columns='date').swaplevel(axis=1).sort_index(axis=1)
tmp[tmp.isna()] = tmp.groupby(level=0, axis=1).transform('mean').ffill(axis=1)
tmp = tmp.astype(int).droplevel(0, axis=1)

# Fix the columns
tmp = tmp.set_axis(np.arange(1, tmp.shape[1] + 1).astype(str), axis=1).add_prefix('val')

Output:

>>> tmp
    val1  val2  val3  val4  val5  val6  val7  val8  val9
id                                                      
1     10    30    50    30    30    30   100    30    10
2     20   -20   120    30   -30   300   100   100   100
3     40   -40   140    50   -50   150    60   -60   160
Admin1

IIUC, compute the cartesian product between id and date to fill missing dates then use your code:

mi = pd.MultiIndex.from_product([df['id'].unique(), df['date'].unique()], names=['id', 'date'])
df = df.set_index(['id', 'date']).reindex(mi).sort_index().ffill()

# Your code
df = df.groupby(level='id').apply(np.ravel).apply(pd.Series).add_prefix('val')

Output:

>>> df
    val0  val1   val2  val3  val4   val5   val6  val7   val8
id                                                          
1   10.0  30.0   50.0  10.0  30.0   50.0  100.0  30.0   10.0
2   20.0 -20.0  120.0  30.0 -30.0  300.0   30.0 -30.0  300.0
3   40.0 -40.0  140.0  50.0 -50.0  150.0   60.0 -60.0  160.0
user_152399510
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