CODEWITHSUNDEEP
pythonnested-lists
vintagedeek
vintagedeek

Reputation: 171

Python - comparing two nested lists and writing a third nested list

some_list = [[app_num, product, prod_size, prod_amt]]
other_list = [[app_num, product, prod_size, prod_amt]]

I have two lists of lists. There are no matches between some_list and other_list for app_num. However, for a given app_num in other_list, the product, prod_size_ and prod_amt may be the same as in a given app_num in some_list. I am trying to create a final_some_list that is the same as some_list, except that it has deleted any list element from some_list if that list element has the same product, prod_size, and prod_amt as an element in other_list.

I have tried nested for loops, list comprehension (below are some examples of many failed attempts). 

final_some_list = [app for app in some_list for other_app in other_list 
if not app[1] == other_app[1] and app[2] == other_app[2] and app[3] == 
other_app[3]

final_some_list = [app for app in some_list for other_app in other_list 
if not app[1] and app[2] and app[3] == in other_app

Upvotes: 2

Views: 906

Answers (2)

Elmex80s
Elmex80s

Reputation: 3504

final_some_list = [x for x in some_list if all(x[1:] != y[1:] for y in other_list)]

Edit:

Solution above is O(nm) where n == len(some_list) and m == len(other_list). You can make it O(n log m) if you want. Put all the tails of all the elements of other_list in a binary search tree (assuming those elements are ordable), now querying that tree is O(log m). In case the elements are hashable you can even have an O(n) solution because querying a hash-set is O(1).

Btw: The elements of both lists look like tuples to me, this will get you more close to a better solution.

Upvotes: 4

pale bone
pale bone

Reputation: 1836

Only the first comparison contains the notattribute, add != to all of the comparisons and this should work:

final_some_list = [app for app in some_list for other_app in other_list 
if app[1] != other_app[1] and app[2] != other_app[2] and app[3] != 
other_app[3]]

Upvotes: 0

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