How to concat several rows in pandas dataframe into 1 row

Question

I need to concat several rows (up to 10) in pandas dataframe to a single row.

For example: I have such dataframe

   a  b
0  1  3
1  2  4

convert to

   a_0  b_0  a_1  b_1 
0  1    3    2    4

Merging row by row is stupid, but I have no idea how to proceed.

Answer 1

Use DataFrame.stack for MultiIndex Series , convert to one row DataFrame and last flatten MultiIndex :

df = df.stack().to_frame().T
df.columns = df.columns.map(lambda x: f'{x[1]}_{x[0]}')
print (df)
   a_0  b_0  a_1  b_1
0    1    3    2    4

Or if all values are numeric use numpy.ravel with itertools.product :

from  itertools import product

c = [f'{x[0]}_{x[1]}' for x in product(df.columns, df.index)]
df = pd.DataFrame([df.to_numpy().ravel()], columns=c)
print (df)
   a_0  a_1  b_0  b_1
0    1    3    2    4