List comprehension: Multiply each string to a single list

Question

I have a list of strings and want to get a new list consisting on each element a number of times.

lst = ['abc', '123']
n = 3

I can do that with a for loop:

res = []
for i in lst:
    res = res + [i]*n
print( res )

['abc', 'abc', 'abc', '123', '123', '123']

How do I do it with list comprehension?

My best try so far:

[ [i]*n for i in ['abc', '123']  ]
[['abc', 'abc', 'abc'], ['123', '123', '123']]

score 8 · Accepted Answer · edited Sep 27 '17 at 05:57

8

>>> lst = ['abc', '123']
>>> n = 3
>>> [i for i in lst for j in range(n)]
['abc', 'abc', 'abc', '123', '123', '123']

The idea behind this is, you loop through the list twice and you print each of the element thrice.

edited Sep 27 '17 at 05:57

Graham

answered Jul 23 '16 at 16:03

Bhargav Rao

Side comment: I understand that wouldn't be a nested list? e.g. `[[1,2],[3,4]]`... – Luis Jul 23 '16 at 18:30
@Luis Yes, To get a nested list you need to add another pair of brackets. Something like this `[[i for j in range(n)] for i in lst]`. Take an hour off and go through those links. They are one of the best docs and will help you understand list-comps better. All the best. – Bhargav Rao Jul 23 '16 at 18:33

score 1 · Answer 2 · answered Jul 23 '16 at 16:37

1

It can also be done as:

>>> lst = ['abc', '123']
>>> n=3
>>> [j for i in lst for j in (i,)*n]
['abc', 'abc', 'abc', '123', '123', '123']

answered Jul 23 '16 at 16:37

shiva

2 Answers2