CODEWITHSUNDEEP
pythonpandas
cjm2671
cjm2671

Reputation: 19486

How do I union update two dataframes?

I have two dataframes, df_original and df_update, both with multiindex.

I want to update df_original with the values of df_update where keys match, and append any new data from df_update to df_original.

How do I do this?

(I've tried df.update and df.merge but can't seem to find a clean solution).

Upvotes: 1

Views: 85

Answers (2)

user2285236
user2285236

Reputation:

Your description matches with the description of the combine_first method:

Combine two DataFrame objects and default to non-null values in frame calling the method. Result index columns will be the union of the respective indexes and columns

Parameters: other : DataFrame

Returns: combined : DataFrame

idx = pd.MultiIndex.from_tuples([('a', 'x'), ('a', 'y'), ('b', 'x')])
df1 = pd.DataFrame([1, 2, 3], index=idx)

df1
Out: 
     0
a x  1
  y  2
b x  3


idx = pd.MultiIndex.from_tuples([('a', 'y'), ('b', 'x'), ('b', 'y')])
df2 = pd.DataFrame([4, 5, 6], index=idx)

df2
Out: 
     0
a y  4
b x  5
  y  6

df1.combine_first(df2)
Out: 
       0
a x  1.0
  y  2.0
b x  3.0
  y  6.0

Upvotes: 1

Nimish Bansal
Nimish Bansal

Reputation: 1759

print(df_original.merge(df_update,how="outer"))

I think this would work

Upvotes: 0

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