samedi 10 novembre 2018

How to select a single random row in one to many matching for left join in pandas

Is there a nice way to bring only one row, preferably random in one-to-many matching during left join in Pandas?

e.g

left = [[1,1,1], [2,2,2],[3,3,3], [9,9,9], [1,3,2]]
right = [[1,2,2],[1,2,3],[3,2,2], [3,2,9], [3,2,2]]
left = np.asarray(left)
right = np.asarray(right)
left = pd.DataFrame(left)
right = pd.DataFrame(right)
joined_left = left.merge(right, how="left", left_on=[0], right_on=[0])

So this is what we get

   0  1  2
0  1  1  1
1  2  2  2
2  3  3  3
3  9  9  9
4  1  3  2

   0  1  2
0  1  2  2
1  1  2  3
2  3  2  2
3  3  2  9
4  3  2  2

   0  1_x  2_x  1_y  2_y
0  1    1    1  2.0  2.0
1  1    1    1  2.0  3.0
2  2    2    2  NaN  NaN
3  3    3    3  2.0  2.0
4  3    3    3  2.0  9.0
5  3    3    3  2.0  2.0
6  9    9    9  NaN  NaN
7  1    3    2  2.0  2.0
8  1    3    2  2.0  3.0

So now I want to have output to be of the same size as my left dataframe and when there are more than one match in right dataframe I want to bring only single random column.

Is there a nice way of doing it using pandas short cut tricks?

thank you!




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