CODEWITHSUNDEEP
pythonarraylist
Prashant Kumar
Prashant Kumar

Reputation: 701

How to maintain sequence of output list while finding the difference of 2 lists

I have to find the difference between a list with another list.

But this process of finding the difference totally randomizes my output every time I run.

Below is my script

getALL = ["apple","ball","cat","dog","eagle"]  // initial list


Sourcee = ["eagle", "ball"]
diff = list(set(getALL) - set(Sourcee))
for items in diff:
    print(items)

Is there any way to keep the sequence of the the diff list same as getALL?

I want my output like this:

apple
cat
dog

Upvotes: 3

Views: 185

Answers (3)

Sunitha
Sunitha

Reputation: 12015

Just a list comprehension would work. Optionally converting Sourcee to a set would make it faster

>>> source_set = set(Sourcee)
>>> [e for e in getALL if e not in source_set]
['apple', 'cat', 'dog']

Upvotes: 5

Jurgen Strydom
Jurgen Strydom

Reputation: 3930

The set operation does not preserve order. However what you can do is to re-build the diff list, by checking what the order was in the original list. This works for any arbitrary order. If the original list contains duplicates this complicates matters.

getALL = ["apple","ball","cat","dog","eagle"]  # initial list


Sourcee = ["eagle", "ball"]
diff = list(set(getALL) - set(Sourcee))

original_order_diff = [x for x in getALL if x in diff]

print(original_order_diff)

Upvotes: 3

U13-Forward
U13-Forward

Reputation: 71570

Use sorted:

diff = list(set(getALL) - set(Source))
for items in sorted(diff, key=getALL.index):
    print(items)

Even tho:

print('\n'.join([i for i in getALL if i not in Source]))

And:

print(*[i for i in getALL if i not in Source], sep='\n')

Would be the shortest solutions.

They all output:

apple
cat
dog

Upvotes: 2

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