CODEWITHSUNDEEP
python
DougKruger
DougKruger

Reputation: 4624

Python way of doing difference of lists containing lists

Consider two lists A and B. I know that list(set(A) - set(B)) will give the difference between A and B. What about the situation whereby elements in both A and B are lists. i.e. A and B are list of list? For e.g.

A = [[1,2], [3,4], [5,6]]
B = [[3,4], [7,8]]

I wish to return the difference A - B as a list of list i.e. [[1,2],[5,6]]

list(set(A) - set(B))
TypeError: unhashable type: 'list'

Upvotes: 1

Views: 64

Answers (4)

Israel Unterman
Israel Unterman

Reputation: 13510

The idea is to convert the list of lists to lists of tuples,
which are hashable and are, thus, candidates of making sets themselves:

In [192]: C = set(map(tuple, A)) - set(map(tuple, B))

In [193]: C
Out[193]: {(1, 2), (5, 6)}

And one more touch:

In [196]: [*map(list, C)]
Out[196]: [[1, 2], [5, 6]]

ADDED

In python 2.7 the final touch is simpler:

map(list, C)

Upvotes: 1

BPL
BPL

Reputation: 9863

A = [[1, 2], [3, 4], [5, 6]]
B = [[3, 4], [7, 8]]

print[x for x in A if x not in B]

Upvotes: 1

Ahasanul Haque
Ahasanul Haque

Reputation: 11134

>>> [i for i in A if i not in B]
[[1, 2], [5, 6]]

Upvotes: 1

gowrath
gowrath

Reputation: 3224

Here's a one-liner you could use:

diff = [x for x in A if x not in B]

Or if you want to use filter:

diff = list(filter(lambda x: x not in B, A))

Upvotes: 1

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