Combine column counts from different dataframes pandas

Question

I have two dataframes. One has demographics information about patients and other has some feature information. Below is some dummy data representing my dataset:

Demographics:

demographics = {
  'PatientID': [10, 11, 12, 13],
  'DOB': ['1971-10-23', '1969-06-18', '1973-04-20', '1971-05-31'],
  'Sex': ['M', 'M', 'F', 'M'],
  'Flag': [0, 1, 0, 0]
}
demographics = pd.DataFrame(demographics)
demographics['DOB'] = pd.to_datetime(demographics['DOB'])

Here is the printed dataframe:

print(demographics)
   PatientID        DOB Sex  Flag
0         10 1971-10-23   M     0
1         11 1969-06-18   M     1
2         12 1973-04-20   F     0
3         13 1971-05-31   M     0

Features:

features = {
  'PatientID': [10, 10, 10, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12],
  'Feature': ['A', 'B', 'A', 'A', 'C', 'B', 'C', 'A', 'B', 'B', 'A', 'C', 'D', 'A', 'B', 'C', 'C', 'D', 'D', 'D', 'B', 'C', 'C', 'C', 'B', 'B', 'C'],
}
features = pd.DataFrame(features)

Here is a count of each features of each patient:

print(features.groupby(['PatientID', 'Feature']).size())
PatientID  Feature
10         A          3
           B          2
           C          2
11         A          3
           B          3
           C          3
           D          1
12         B          3
           C          4
           D          3
dtype: int64

I want to integrate each patients feature counts of their features into the demographics table. Note that patient 13 is absent from the features table. The final dataframe will look as shown below:

result = {
  'PatientID': [10, 11, 12, 13],
  'DOB': ['1971-10-23', '1969-06-18', '1973-04-20', '1971-05-31'],
  'Feature_A': [3, 3, 0, 0],
  'Feature_B': [2, 3, 3, 0],
  'Feature_C': [2, 3, 4, 0],
  'Feature_D': [0, 1, 3, 0],
  'Sex': ['M', 'M', 'F', 'M'],
  'Flag': [0, 1, 0, 0],
  }
  
result = pd.DataFrame(result)
result['DOB'] = pd.to_datetime(result['DOB'])

print(result)
   PatientID        DOB  Feature_A  Feature_B  Feature_C  Feature_D Sex  Flag
0         10 1971-10-23          3          2          2          0   M     0
1         11 1969-06-18          3          3          3          1   M     1
2         12 1973-04-20          0          3          4          3   F     0
3         13 1971-05-31          0          0          0          0   M     0

How can I get this result from these two dataframes?

Answer 1

Cross-tabulate features and merge with demographics .

# cross-tabulate feature df 
# and reindex it by PatientID to carry PatientIDs without features
feature_counts = (
    pd.crosstab(features['PatientID'], features['Feature'])
    .add_prefix('Feature_')
    .reindex(demographics['PatientID'], fill_value=0)
)
# merge the two
demographics.merge(feature_counts, on='PatientID')

Answer 2

Fix your code adding unstack

out = (features.groupby(['PatientID', 'Feature']).size().
       unstack(fill_value=0).
       add_prefix('Feature_').
       reindex(demographics['PatientID'],fill_value=0).
       reset_index().
       merge(demographics))
Out[30]: 
   PatientID  Feature_A  Feature_B  Feature_C  Feature_D        DOB Sex  Flag
0         10          3          2          2          0 1971-10-23   M     0
1         11          3          3          3          1 1969-06-18   M     1
2         12          0          3          4          3 1973-04-20   F     0
3         13          0          0          0          0 1971-05-31   M     0