Converting to str a numpy and join with pandas series

Question

I need help to add some random integers and some prefixed str to a pandas series. I' ll better explain: I' ve got my pandas series called variables and would like to add to it random integers from 1 to 10 and also a plus and a space. Let' s say at a given row of my pandas series I have value x1 and I want to add (meant as join) to it the corresponding value, let's say 1, from a generated numpy array of random numbers but also put a space in between and a plus before them. This is what I want to obtain:

+1 x1

This is what I did:

import numpy as np
coeff = np.random.randint(1, 11, variables.shape[0])
coeff = coeff.astype(str)
monom = '+' + coeff + ' ' + variables

But it returns this error:

ufunc 'add' did not contain a loop with signature matching types (dtype('<U11'), dtype('<U11')) -> dtype('<U11')

Would someone know how to help me? I' m also open in changing the way of doing it, I just need some random numbers generated but not necessarily need to pass for numpy.

Answer 1

Just convert coeff into a string Series:

import pandas as pd
import numpy as np

# dummy series for setup
variables = pd.Series(list('abcde'))

# create new random Series
coeff = pd.Series(np.random.randint(1, 11, variables.shape[0]), dtype=str)

# add
monom = '+' + coeff + ' ' + variables.astype(str)

print(monom)

Output

0     +8 a
1     +2 b
2    +10 c
3     +3 d
4     +8 e
dtype: string

As an alternative you could use the str.cat method:

monom = '+' + coeff.str.cat(variables.astype(str), sep=' ')