dataframe merge

[deanhystad]

It appears to be straight forward. The "trick" is only merging some columns from the second dataframe. This can be accomplished by merging a dataframe that only contains the columns you want to merge.

The code below uses a dataframe slice that only has the PZN and MB columns.

import pandas as pd
from io import StringIO

data1 = StringIO(
    """PZN|Name|Anzahl
1234|Aspirin|1
2345|Mexalen|2
4567|Sinupret|9
4567|Sinupret|2
"""
)
data2 = StringIO(
    """PZN|MB|Zeichen
1234|1|+
2345|2|++
4567|0|++
"""
)

df1 = pd.read_csv(data1, sep="|")
df2 = pd.read_csv(data2, sep="|")
print(df1)
print(df2)  # All columns
print(df2[["PZN", "MB"]])  # Only PZN and MB columns
df3 = df1.merge(df2[["PZN", "MB"]], on="PZN")
print(df3)

Output:
    PZN      Name  Anzahl
0  1234   Aspirin       1
1  2345   Mexalen       2
2  4567  Sinupret       9
3  4567  Sinupret       2
    PZN  MB Zeichen
0  1234   1       +
1  2345   2      ++
2  4567   0      ++
    PZN  MB
0  1234   1
1  2345   2
2  4567   0
    PZN      Name  Anzahl  MB
0  1234   Aspirin       1   1
1  2345   Mexalen       2   2
2  4567  Sinupret       9   0
3  4567  Sinupret       2   0

Is that the desired output?

Are you reading the data from a csv file? The whitespace around the "|" are a problem. If my data looks like this:

Output:
data1 = StringIO(
    """PZN | Name | Anzahl
1234|Aspirin|1
2345|Mexalen|2
4567|Sinupret|9
4567|Sinupret|2
"""
)
data2 = StringIO(
    """PZN|MB|Zeichen
1234|1|+
2345|2|++
4567|0|++
"""
)

I get an error on the merge because one table has "PZN " as a header and the other has "PZN". The best way to fix the problem is clean it up in the files.