How to solve Empty Dataframe problem when I merge two dataframes?

Question

The following is my code:

np.random.seed(0)
left = pd.DataFrame({'key': ['A', 'B', 'C', 'D'], 'value': np.random.randn(4)})    
right = pd.DataFrame({'key': ['B', 'D', 'E', 'F'], 'value': np.random.randn(4)})
print(pd.merge(left,right))

The result is:

Empty DataFrame
Columns: [key, value]
Index: []

I don't know why they are empty.

What data is in your dataframes? Maybe there are no matching values between them? — NotAName
– NotAName, Commented Mar 11, 2021 at 0:02
Use on= parameter: print(pd.merge(left,right, on='key')) — Andrej Kesely
– Andrej Kesely, Commented Mar 11, 2021 at 0:02

mhawke · Accepted Answer · 2021-03-11 00:05:58Z

2

Try specifying the column on which to join like this:

>>> pd.merge(left, right, on='key')
  key   value_x   value_y
0   B  0.400157  1.867558
1   D  2.240893 -0.977278

If you require all keys:

>>> pd.merge(left, right, on='key', how='outer')
  key   value_x   value_y
0   A  1.764052       NaN
1   B  0.400157  1.867558
2   C  0.978738       NaN
3   D  2.240893 -0.977278
4   E       NaN  0.950088
5   F       NaN -0.151357

answered Mar 11, 2021 at 0:05

mhawke

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