Pandas KeyError: when merging 2 dataframes

Question

I am trying to merge 2 columns from DF2 to DF1 (Note DF2 has multiple columns). I am merging these columns on "Unique ID".

When I do so I get the following error KeyError: 'Unique ID'

I have read online that the KeyError error can be caused by indexing issues, and not using the exact column names. However I have reset the index and I have checked and double checked that the column we're merging on ("Unique ID") is in both DF1 and DF2.

I would rather not share the DFs as they contain sensitive information

This is the code I am using

df = pd.merge(DF1,DF2[['System','Platform']],on='Unique ID', how='left')

you are only using the columns 'Segment' and 'Platform' from the DF2? So it cannot find 'Unique ID' in the second dataframe. — Paul
– Paul, Commented Dec 1, 2021 at 10:07
@Paul I have updated the question. I am merging the system and platform column for DF2 to DF1 — PythonBeginner
– PythonBeginner, Commented Dec 1, 2021 at 10:09

Paul · Accepted Answer · 2021-12-01 10:08:52Z

6

Try:

df = pd.merge(DF1,DF2[['System','Platform', 'Unique ID']],on='Unique ID', how='left')

answered Dec 1, 2021 at 10:08

Paul

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2 Comments

PythonBeginner Over a year ago

why do you need to specify the first unique ID

Paul Over a year ago

The column you are merging on should be in both dataframes. DF2[['System','Platform']] returns a dataframe without 'Unique ID', so it cannot match that column with the Unique ID column in DF1.

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