Reputation: 2621
I've a list of lists, in which each element is a single character:
ngrams = [['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c'],
['a', 'a', 'a', 'b', 'b', 'b', 'c', 'c', 'c']]
From this, I want to generate a new single list with the content ['aa','ab','ac','ba','bb','bc','ca','cb','cc']
. The individual elements of each list are appended to each other but in reverse order of the lists. I've come up with this (where np = 2
):
for cnt in range(np-2,-1,-1):
thisngrams[-1] = [a+b for (a,b) in zip(thisngrams[-1],thisngrams[cnt])]
My solution needs to handle np
higher than just 2. I expect this is O(np), which isn't bad. Can someone suggest a more efficient and pythonic way to do what I want (or is this a good pythonic approach)?
Upvotes: 1
Views: 86
Reputation: 71471
You can try this:
ngrams = [['a', 'b', 'c', 'a', 'b', 'c', 'a', 'b', 'c'],
['a', 'a', 'a', 'b', 'b', 'b', 'c', 'c', 'c']]
new = map(''.join, zip(*ngrams))
Output:
['aa', 'ba', 'ca', 'ab', 'bb', 'cb', 'ac', 'bc', 'cc']
For more than two elements:
n = [["a", "b", "c"], ["a", "c", "d"], ["e", "f", "g"]]
new = map(''.join, zip(* reversed(ngrams)))
#in Python3
#new = list(map(''.join, zip(* reversed(ngrams))))
Output:
['eaa', 'fcb', 'gdc']
Upvotes: 5