pd.merge question. how=left creates more observations?

Asked Jul 14 '21 at 20:23

Active Jul 14 '21 at 21:00

Viewed 19 times

print(len(df))
264764

df = df.merge(df2[['id','Re']], on=['id'], suffixes=('', '_fwd1'), how='left')
print(len(df))
2714684

why would this result in more data than df originally had? Even when i do how='inner' which should be the intersection of keys i get more observations.

edited Jul 14 '21 at 21:00

martineau

112,593
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asked Jul 14 '21 at 20:23

ben shapiro

The keys in `df` likely match multiple rows in `df2`. – not_speshal Jul 14 '21 at 20:27
Does this answer your question? [Pandas Left Outer Join results in table larger than left table](https://stackoverflow.com/questions/22720739/pandas-left-outer-join-results-in-table-larger-than-left-table) – not_speshal Jul 14 '21 at 20:27
I'll take a look, id's should have been unique but your answer makes sense – ben shapiro Jul 14 '21 at 20:29

pd.merge question. how=left creates more observations?

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