Subtract two lists of tuples from each other

Question

I have the these two lists and I need to subtract one from the other but the regular "-" won't work, neither will .intersection or XOR (^).

A = [(0, 1)]
B = [(0, 0), (0,1), (0, 2)]

Essentially what I want is:

B - A = [(0, 0), (0, 2)]

score 3 · Answer 1 · edited May 23 '17 at 12:24

3

You can use list comprehension to solve this problem:

[item for item in B if item not in A]

More discussion can be found here

edited May 23 '17 at 12:24

Community

answered Sep 18 '16 at 15:58

nbryans

Moses Koledoye · Answer 2 · 2016-09-18T16:12:04.150

2

If there are no duplicate tuples in B and A, might be better to keep them as sets, and use the difference of sets:

A = [(0, 1)]
B = [(0, 0), (0,1), (0, 2)]
diff = set(B) - set(A) # or set(B).difference(A)
print(diff)
# {(0, 0), (0, 2)}

You could perform other operations like find the intersection between both sets:

>>> set(B) & set(A)
{(0, 1)}

>>> set(B) ^ set(A)
{(0, 0), (0, 2)}

edited Sep 18 '16 at 16:12

answered Sep 18 '16 at 16:00

Moses Koledoye

When using methods like `.difference` you don't explicitly need to convert `A` to a set as it'll take any iterable. – Jon Clements Sep 18 '16 at 16:09

score 0 · Answer 3 · edited May 23 '17 at 12:24

0

You can do such operations by converting the lists to sets. Set difference:

r = set(B)-set(A)

Convert to list if necessary: list(r)

Working on sets is efficient compared to running "in" operations on lists: using lists vs sets for list differences

edited May 23 '17 at 12:24

Community

answered Sep 18 '16 at 16:09

picmate 涅

3 Answers3