CODEWITHSUNDEEP
pythonlistnestedloops
ethann
ethann

Reputation: 209

Nesting lists in for loop in python

I am iterating through a for loop looking for keyword matches in a list and then compiling the match indices to a third list. I can compile the indices as a list of lists, but I want to further group sub-lists by the item they matched.

import re, itertools
my_list = ['ab','cde']
keywords = ['ab','cd','de']

indices=[]
pats = [re.compile(i) for i in keywords]
for pat in pats:
    for i in my_list:
        for m in re.finditer(pat, i):
            a =list((m.start(),m.end()))
            indices.append(a)
print(indices)

This returns:

[[0, 2], [0, 2], [1, 3]]

Trying to get:

[[0, 2], [[0, 2], [1, 3]]]

so that it is clear that:

[[0, 2], [1, 3]]

are indices matches on 'cde' in the example above.

Upvotes: 1

Views: 187

Answers (2)

Piotr Hajduga
Piotr Hajduga

Reputation: 608

Make indices a dict:

import re, itertools
my_list = ['ab','cde']
keywords = ['ab','cd','de']

indices = {}
pats = [re.compile(i) for i in keywords]
for pat in pats:
    for i in my_list:
        indices.setdefault(i, [])
        for m in re.finditer(pat, i):
            a = list((m.start(),m.end()))
            indices[i].append(a)
print(indices)

Giving:

{'cde': [[0, 2], [1, 3]], 'ab': [[0, 2]]}

Is this what you're looking for?

I played with this code for a while and since you import itertools you might as well use it to get rid off those ugly nested fors ;) like that:

import re
from itertools import product

my_list = ['ab', 'cde']
keywords = ['ab', 'cd', 'de']

indices = {}
pats = [re.compile(i) for i in keywords]

for i, pat in product(my_list, pats):
    indices.setdefault(i, [])
    for m in re.finditer(pat, i):
        indices[i].append((m.start(), m.end()))

print(indices)

Unfortunately I can't get Bakuriu's idea to use list comprehension to work properly. So for now this seems like the best solution to me.

Upvotes: 2

Bakuriu
Bakuriu

Reputation: 101909

Create a list for each match and accumulate the matches in this list, finally add it to the result:

import re, itertools
my_list = ['ab','cde']
keywords = ['ab','cd','de']

indices=[]
pats = [re.compile(i) for i in keywords]
for pat in pats:
    for i in my_list:
        sublist = []
        for m in re.finditer(pat, i):
            a =list((m.start(),m.end()))
            sublist.append(a)
        indices.append(sublist)
print(indices)

Or you could use a list-comprehension:

import re, itertools
my_list = ['ab','cde']
keywords = ['ab','cd','de']

indices=[]
pats = [re.compile(i) for i in keywords]
for pat in pats:
    for i in my_list:
        sublist = [(m.start(), m.end()) for m in re.finditer(pat, i)]
        indices.append(sublist)
print(indices)

Upvotes: 0

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