how to add values to certain index in column in pandas dataframe (python)

Question

I have a dataframe (results) like this:

index	results
0	1
1	-1
2	1

I have another dataframe (signals) like this:

index	signals
0	200
1	300
2	250
3	450
4	345
5	534

I want to add a column in signals such that the value from results will be copied twice in that column like

index	signals	results
0	200	1
1	300	1
2	250	-1
3	450	-1
4	345	1
5	534	1

Note: The 1 from index 0 from results is copied twice in index 0 and 1 of signals and so on. How can i go about doing this?

Answer 1

IIUC, you just want to repeat results twice and assign it to a column in signals , right? In that case, you can use, np.repeat :

import numpy as np
signals['results'] = np.repeat(results['results'].to_numpy(), 2)

Output:

   index  signals  results
0      0      200        1
1      1      300        1
2      2      250       -1
3      3      450       -1
4      4      345        1
5      5      534        1

Answer 2

The @mozway's answer is more relevant than mine because he uses Series.repeat instead Index.repeat . The @Manlai's answer is interesting too.

Use Index.repeat :

n = len(signals) // len(results)  # twice
signals['results'] = results.reindex(results.index.repeat(n)).to_numpy()
print(signals)

# Output
   signals  results
0      200        1
1      300        1
2      250       -1
3      450       -1
4      345        1
5      534        1

Answer 3

Keep it simple, just use the Series' repeat method:

n = len(signals) // len(results)
signals['results'] = result['results'].repeat(n).to_numpy()

output:

   index   signals  results
0       0      200        1
1       1      300        1
2       2      250       -1
3       3      450       -1
4       4      345        1
5       5      534        1