How to assign a slice to a slice in a Pandas dataframe?

Question

Having:

np.random.seed(42)
df_one = pd.DataFrame(np.random.rand(4,3), columns=['colA', 'colB', 'colC'])

And:

df_two = pd.DataFrame(np.ones([2,3]), columns=['colA', 'colB', 'colC'])

When I try to assign, like this:

df_one.loc[2:4, 'colB'] = df_two.loc[:, 'colB']

I get:

colA    colB    colC
0.37    0.95    0.73
0.59    0.15    0.15
0.05    NaN     0.60
0.70    NaN     0.96

When expecting to get:

colA    colB    colC
0.37    0.95    0.73
0.59    0.15    0.15
0.05    1.0     0.60
0.70    1.0     0.96

Answer 1

This can be done adding a to_list() at the end:

df_one.loc[2:4, 'colB'] = df_two.loc[:, 'colB'].to_list()

Or:

df_one.loc[2:4, 'colB'] = df_two.loc[:, 'colB'].values