CODEWITHSUNDEEP
pythonpandasjoinmergemulti-index
rpb
rpb

Reputation: 3299

Unable to join to dataframe in pandas

I have two df. The first df is a multiindex and the other one is typical single index.

enter image description here

Figure 1: Multiindex df

and

enter image description here

Figure 2: Single indexing

Upon join these two df, I got the following error

cannot join with no overlapping index names

I suspect, this error due to the index column name in the first df (Figure 1).

Even, swaping the index name and typical numeric value also does not help

enter image description here

Figure 2: Multiindex df

May I know how to address this error?

Thanks in advance for the time taken

Upvotes: 3

Views: 25547

Answers (2)

flipflipped
flipflipped

Reputation: 31

If you are trying to do a function such as df.rolling(window).cov()/df.rolling(window).var() where you are trying to basically merge two multi-index dataframes what happened to me was I had to specify a name to the index as it doesn't know they name of the index to match on which is why you are getting this error. If you are using something like yfin to get data you won't run into this issue because the index always defaults as 'Date'. Here is a simple one-liner to fix this:

df.index.rename('Date', inplace=True)

Upvotes: 1

jezrael
jezrael

Reputation: 862581

You can convert first level in MultiIndex to column before merge:

df = (df1.reset_index(level=0)
         .merge(df2, left_index=True, right_index=True)
         .set_index('name', append=True)
         .swaplevel(1, 0))

Or if use join:

df = df1.reset_index(level=0).join(df2).set_index('name', append=True).swaplevel(1, 0)

Upvotes: 7

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