Best way to multiply string by array

Question

I want to repeat each character in my string by a number I have in an array i.e. if

rep = [1, 0, 1, 1, 3, 0, 0, 1, 0]
seq = 'AATCGGGAA'

I want something like

seq*rep

to output

ATCGGGA

score 6 · Answer 1 · answered Jul 07 '14 at 14:45

You can use zip, a list comprehension, and str.join:

>>> rep = [1, 0, 1, 1, 3, 0, 0, 1, 0]
>>> seq = 'AATCGGGAA'
>>>
>>> list(zip(seq, rep)) # zip pairs up the items in the two lists
[('A', 1), ('A', 0), ('T', 1), ('C', 1), ('G', 3), ('G', 0), ('G', 0), ('A', 1), ('A', 0)]
>>>
>>> ''.join([x*y for x,y in zip(seq, rep)])
'ATCGGGA'
>>>

score 4 · Accepted Answer · answered Jul 07 '14 at 14:49

4

Fastest way to do this will be to use map with operator.mul:

>>> from operator import mul
>>> ''.join(map(mul, seq, rep))
'ATCGGGA'

answered Jul 07 '14 at 14:49

Ashwini Chaudhary

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What do you mean by fastest, i.e. most efficient? least number of keystrokes? – bdeonovic Jul 07 '14 at 14:51
Good find! I appreciate the diversity of answers one can get from SO – bdeonovic Jul 07 '14 at 14:58
So which one wins if you user [`itertools.izip()`](https://docs.python.org/2/library/itertools.html#itertools.izip) (or just regular `zip` in python 3)? – Jamie Cockburn Jul 07 '14 at 15:18

score 2 · Answer 3 · answered Jul 07 '14 at 14:46

2

This should do the trick:

"".join([s*r for r, s in zip(rep, seq)])

Output:

"ATCGGGA"

answered Jul 07 '14 at 14:46

Jamie Cockburn

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1

@iCodez beat you to it :) thanks for the answer though – bdeonovic Jul 07 '14 at 14:50

Best way to multiply string by array

3 Answers3