[FIXED] Why do I have less rows when I merge using "outer" argument?

Issue

The shape of fd is (315360, 4) and fd2's shape is (214704, 4).

df:

Country	Partner Country	Year	Variable1
Turkey	Spain	1993	183188
Spain	Turkey	1993	3918281
US	UK	1993	495949282
US	UK	1994	495949282
UK	US	1994	495949282

df2:

Country	Partner Country	Year	Variable2
Syria	Spain	1993	183188
Turkey	Spain	1993	3918281
US	UK	1993	495949282
Germany	UK	1994	495949282
UK	US	1994	495949282

df.merge(df2, how="outer", on=["Country", "Partner Country", "Year"])

data shape I get after the merge is (351351, 5). Why is not (530064, 5) and how can I have this without losing any info.

Solution

You can use concat with drop_duplicates:

df = pd.concat([df, df2]).drop_duplicates()

Answered By - Fastnlight