Lengthening a DataFrame based on stacking columns within it in Pandas

Question

I am looking for a function that achieves the following. It is best shown in an example. Consider:

pd.DataFrame([ [1, 2, 3 ], [4, 5, np.nan ]], columns=[\'x\', \         


        

Answer 1

You can use stack to get things done i.e

pd.DataFrame(df.set_index('x').stack().reset_index(level=0).values,columns=['x','y'])

     x    y
0  1.0  2.0
1  1.0  3.0
2  4.0  5.0