Element wise concatenate multiple lists (list of list of strings)

Question

i have a list of list of strings as below

lst = [['a','b','c'],['@','$','#'],['1','2','3']]

I want to concatenate each string inside the lists element wise, expected output as below:

['a@1','b$2','c#3']

The size of lst can vary. is there any way to accomplish this without going through for loops.
I tried to use map, but its not working.

map(str.__add__,(x for x in list))

please help.

Answer 1

Here's one way zipping the sublists and mapping with ''.join the resulting tuples:

list(map(''.join, zip(*lst)))
# ['a@1', 'b$2', 'c#3']

---

Here zip as shown in the docs aggregates elements from several iterables. With *, we are unpacking the list into separate iterables, which means that the function will instead be receiving zip(['a','b','c'],['@','$','#'],['1','2','3']).

Now at each iteration, map will be applying ''.join to each of the aggregated iterables, i.e to the first element in each sublist, then the second, and so on.

Answer 2

Not as elegant as yatu's answer but if you're using pandas:

import pandas as pd
pd.DataFrame(lst).sum(axis=0)

# 0    a@1
# 1    b$2
# 2    c#3
# dtype: object

Pandas Series have a .tolist() method to get the expected output:

series = pd.DataFrame(lst).sum(axis=0)
series.tolist()

# ['a@1', 'b$2', 'c#3']