I want to merge two CSV files from the open Bixi dataset. The problem is that after the outer merge, there are rows missing:

In [148]: outer_merged_df['Code']==7150
Out[148]: 
0          False
1          False
2          False
3          False
4          False
           ...  
1045584    False
1045585    False
1045586    False
1045587    False
1045588    False
Name: Code, Length: 1045589, dtype: bool

But this row is present in the left dataset:

In [151]: df['Code']==7150
...
615     True

Here is the code for the outer merge:

outer_merged_df = pd.merge(df, df_ride, left_on='Code', right_on='start_station_code', how='outer', indicator=True)

Here is the code to read the Bixi rides and the station:

df_ride = pd.read_csv('OD_2019-08.csv')
df = pd.read_csv('Stations_2019.csv')

And there is the link to the CSV files. If you’re going to download them, please use the August of 2019 file.

When I do a left merge, it finds it:

In [154]: merged_df_left=pd.merge(df, df_ride, left_on='Code', right_on='start_station_code', how='left')

In [155]: merged_df_left['Code']==7150
Out[155]: 
913466     True
Name: Code, Length: 913470, dtype: bool

This is extremely confusing. Can someone please give a hint?