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pythonlist
Jack Liaiea
Jack Liaiea

Reputation: 67

Find common elements that are in the same order in two lists Python

Just have a quick question about python. I was wondering if there was any simple pythonic way to take two list such as:

a = ['t', 'o', 'a', 'c']
b = ['c', 't', 'a', 'o']

and then return the common elements/chars that are also in the same order relative to each other between the two lists. 

# possible outputs for this list could be either:
output: ['t', 'a']
output: ['t', 'o']

I can initially start with two lists and extract the matching elements while still keeping the order in tact by doing this:

c = ['z', 't', 'o', 'g', 'a', 'c', 'f']
d = ['e', 'q', 'c', 't', 'a', 'o', 'y']
a = [x for x in c if x in d]
b = [x for x in d if x in c]

Which will give me the original a and b lists. However, I wasn't able to find a away to reduce this further. Tried using sets but that doesn't keep the order of the elements. I know an easy way would probably just be brute for and n^2 to compare one list to another in place, but I am trying to avoid that and find a solution that would find the largest match in two lists relative to each other.

Upvotes: 1

Views: 756

Answers (1)

Fabiano
Fabiano

Reputation: 377

>>> import itertools
>>> a = ['t', 'o', 'a', 'c']
>>> b = ['c', 't', 'a', 'o']

>>> [i for i in itertools.combinations(a, 2) if i in  itertools.combinations(b, 2)]

[('t', 'o'), ('t', 'a')]

Edit:

To get all

>>> c = ['z', 't', 'o', 'x', 'a', 'c', 'f', 'g']
>>> d = ['e', 'q', 'c', 't', 'a', 'g', 'o', 'y']

>>> def f(l):
...  r = []
...  for i in range(2, len(l)+1):
...   r += itertools.combinations(l, i)
...  return r
>>>
>>> [i for i in f(c) if i in f(d)]

[('t', 'o'), ('t', 'a'), ('t', 'g'), ('a', 'g'), ('c', 'g'), ('t', 'a', 'g')]

Or:

>>> def f(l):
...     return [j for i in range(2, len(l)+1) for j in list(itertools.combinations(l, i))]
>>>
>>> [i for i in f(c) if i in f(d)]

[('t', 'o'), ('t', 'a'), ('t', 'g'), ('a', 'g'), ('c', 'g'), ('t', 'a', 'g')]

Upvotes: 2

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