Reputation: 19
I need to be able to find differences in list that may have identical values to one another besides two added elements
example
a = ['cool task', 'b', 'another task', 'j', 'better task', 'y']
b = ['cool task', 'b', 'a task', 'j', 'another task', 'j', 'better task', 'y']
How my problem is, both 'a task'
and 'another task'
both are followed by a 'j'
[x for x in b if x not in a]
['a task']
Because both a
and b
contain 'j'
, it is removed from the list.
How would I make so that I end up with
['a task', 'j']
Upvotes: 0
Views: 77
Reputation: 605
it works as you want:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
def difference(a, b):
a, b = (lambda x, y: (y, x) if len(set(x)) > len(set(y)) else (x, y)) (a, b)
a_result = list(a)
b_result = list(b)
for z in range(len(a)):
if a[z] in b:
a_result.remove(a[z])
b_result.remove(a[z])
return a_result, b_result
# or
# return a_result if len(set(a_result)) > len(set(b_result)) else b_result
def main():
a = ['cool task', 'b', 'another task', 'j', 'better task', 'y']
b = ['cool task', 'b', 'a task', 'j', 'another task', 'j', 'better task', 'y']
print(difference(a, b))
if __name__ == "__main__":
main()
Upvotes: 1
Reputation: 1125398
You could use the difflib.SequenceMatcher()
class to enumerate added, removed and changed entries:
>>> from difflib import SequenceMatcher
>>> matcher = SequenceMatcher(a=a, b=b)
>>> added = []
>>> for tag, i1, i2, j1, j2 in matcher.get_opcodes():
... if tag == 'insert':
... added += b[j1:j2]
...
>>> added
['a task', 'j']
The above only focuses on added entries; if you need to know about entries that were removed or altered, then there are opcodes for those events too, see the SequenceMatcher.get_opcodes()
method documentation.
However, if your entries are always paired, then just produce sets with tuples from them (using pair-wise iteration); you can then do any set operations on these:
aset = set(zip(*([iter(a)] * 2)))
bset = set(zip(*([iter(b)] * 2)))
difference = bset - aset
Demo:
>>> aset = set(zip(*([iter(a)] * 2)))
>>> bset = set(zip(*([iter(b)] * 2)))
>>> aset
{('another task', 'j'), ('cool task', 'b'), ('better task', 'y')}
>>> bset
{('a task', 'j'), ('another task', 'j'), ('cool task', 'b'), ('better task', 'y')}
>>> bset - aset
{('a task', 'j')}
Upvotes: 1
Reputation: 52008
Depending on your purposes, you could possibly use Counter
from the collections module:
>>> from collections import Counter
>>> a = Counter(['cool task', 'b', 'another task', 'j', 'better task', 'y'])
>>> b = Counter(['cool task', 'b', 'a task', 'j', 'another task', 'j', 'better task', 'y'])
>>> b-a
Counter({'j': 1, 'a task': 1})
>>> list((b-a).keys())
['j', 'a task']
Upvotes: 0
Reputation: 16224
For simple list - what you ask is simply searching for that next item in the list:
>>> a = ['cool task', 'b', 'another task', 'j', 'better task', 'y']
>>> b = ['cool task', 'b', 'a task', 'j', 'another task', 'j', 'better task', 'y']
>>> c = [[x, b[b.index(x) + 1]] for x in b if x not in a]
>>> c
[['a task', 'j']]
But I think you are actually aiming at using dictionary or tuples.
Tuples:
>>> a = [('cool task', 'b'), ('another task', 'j'), ('better task', 'y')]
>>> b = [('cool task', 'b'), ('a task', 'j'), ('another task', 'j'), ('better task', 'y')]
>>> c = [x for x in b if x not in a]
>>> c
[('a task', 'j')]
Dictionaries:
>>> a = {'cool task': 'b', 'another task': 'j', 'better task': 'y'}
>>> b = {'cool task': 'b', 'a task': 'j', 'another task': 'j', 'better task': 'y'}
>>> c = [(x, b[x]) for x in b if x not in a]
>>> c
[('a task', 'j')]
Upvotes: 1