How to move particular values of one dataframe to another if we cannot use index column?

Question

I have 2 DataFrames: 'data_test' and 'data'. I need to add column 'final_output_ratio' to data_test, but only if value of column 'date' is the same for both (so I need to add only 3 values from data). DataFrames are:

data_test={'date':['2016-09-01 00:59:59','2016-09-01 01:59:59','2016-09-01 02:59:59'],
              'stage_1_output':[0.88,0.91,0.82],
              'stage_2_output':[0.91,0.95,0.87]}
data_test=pd.DataFrame(data=data_test)
data_test

date    stage_1_output  stage_2_output
0   2016-09-01 00:59:59 0.88    0.91
1   2016-09-01 01:59:59 0.91    0.95
2   2016-09-01 02:59:59 0.82    0.87
data={'date':['2016-09-01 00:59:59','2016-09-01 01:59:59','2016-09-01 02:59:59','2017-09-01 02:59:59','2017-09-01 03:14:59'],
              'stage_1_output':[0.88,0.91,0.82,0.88,0.92],
              'stage_2_output':[0.91,0.95,0.87,0.85,0.9],
              'final_output_ratio':[0.22,0.17,0.14,0.18,0.24]   }
data=pd.DataFrame(data=data)

    date    stage_1_output  stage_2_output  final_output_ratio
0   2016-09-01 00:59:59 0.88    0.91    0.22
1   2016-09-01 01:59:59 0.91    0.95    0.17
2   2016-09-01 02:59:59 0.82    0.87    0.14
3   2017-09-01 02:59:59 0.88    0.85    0.18
4   2017-09-01 03:14:59 0.92    0.90    0.24

I am trying this:

data_test['final_output_ratio']=data['final_output_ratio'].loc[data['date']==data_test['date']]

And get an error: ValueError: Can only compare identically-labeled Series objects

What can solve the problem?

Corralien · Accepted Answer · 2021-09-29 12:14:36Z

1

Use pd.merge on date with how='left' parameter:

>>> pd.merge(data_test, data[['date', 'final_output_ratio']], how='left', on='date')

                  date  stage_1_output  stage_2_output  final_output_ratio
0  2016-09-01 00:59:59            0.88            0.91                0.22
1  2016-09-01 01:59:59            0.91            0.95                0.17
2  2016-09-01 02:59:59            0.82            0.87                0.14

answered Sep 29, 2021 at 12:14

Corralien

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