I am new to Python. I have the following code which is a part of a string algorithm that i'm currently developing.
>>> newlist=[]
>>> i =0
>>> for x in range(len(list1)):
new_item = [y for y in list1[i] if y not in list2[i]]
newlist.append(new_item)
i=i+1
>>> print newlist
I like to do this using list comprehension as I've read it is performance optimized. Can somebody suggest me a method.
Thank you.
[Edit]
example:
list1= [[['pat'],['cut'],['rat']], [['sat','pat'],['cut','pat']],[['instructor','plb','error0992'],['instruction','address','00x0993'],['data','address','017x112']]
list2= [[['pat'], ['cut'], ['rat']], [['sat', 'pat']], [['instructor', 'plb', 'error0992'], ['instruction', 'address', '00x0993']]]
So the new list,
newlist= [[], [['cut', 'pat']], [['data', 'address', '017x112']]]
If you just want all elements that are in one list and not in another, I would suggest looking into python sets. They don't allow for duplicates, but the performance and readability benefits are large.
You would implement this like so:
newlist = list(set(list1).difference(set(list2)))
If you want to apply this in place of your current solutions, you should do something along the lines of what Dominic suggested (slightly edited for readability):
[list(set(a)-set(b)) for a, b in zip(list1, list2)]
If the order matters, or you have duplicates, then the single list comprehension you had above should do the trick, just wrap it as a lambda function to make it more readable:
single_item = lambda i: [y for y in list1[i] if y not in list2[i]]
newlist = [single_item(i) for i in enumerate(list1)]