Using a list of lists to filter a list of lists

Question

I have two lists of lists, one that includes all records e.g. [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk'], ['cereal', 'skittles']] and one that contains rules [['milk', 'eggs'], ['milk','ham']].

I'm trying to filter records by the list_of_rules, however, I want to capture [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk']] despite it not exactly matching [['milk', 'eggs'], ['milk','ham']] order and extra items wise.

records = [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk'], ['cereal', 'skittles']]

list_of_rules = [['milk', 'eggs'], ['milk','ham']]

# this list comprehension only filters for exact matches

results = [[x for x in L if x in records] for L in list_of_rules] 


# expected output

print(results)
>>[['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk']]

Any and all recommendations very much appreciated.

Djaouad · Accepted Answer · 2019-04-03 21:07:10Z

1

You can use this list comprehension:

records = [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk'], ['cereal', 'skittles']]

list_of_rules = [['milk', 'eggs'], ['milk','ham']]

results = [L for L in records if any(set(R).issubset(L) for R in list_of_rules)]

print(results) # => [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk']]

It loops for each list of records L and checks whether there exists at least one list of rules R (using the built-in function any) such that R is included in L (using the set method issubset).

edited Apr 3, 2019 at 21:07

answered Apr 3, 2019 at 21:01

Djaouad

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Patrick Artner · Accepted Answer · 2019-04-03 21:01:32Z

0

You can use a list of sets of rules and demand that any rule intersection'ed with a inner list is identical to the set (i.e. all items in the set are also present in the inner list):

records = [['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk'], ['cereal', 'skittles']]

list_of_rules = [{'milk', 'eggs'}, {'milk','ham'}]

# this list comprehension only filters for exact matches

# take the full inner list if all things in any rule are in this inner list
results = [ x for x in records if any( p.intersection(x) == p for p in list_of_rules)  
print(results)

Output:

[['eggs', 'milk', 'butter'], ['ham', 'spam', 'milk']]

answered Apr 3, 2019 at 21:01

Patrick Artner

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