Pythonic way to compare two lists and print out the differences
I have two lists which are guaranteed to be the same length. I want to compare the corresponding values in the list (except the 开发者_Go百科first item) and print out the ones which dont match. The way I am doing it is like this
i = len(list1)
if i == 1:
print 'Nothing to compare'
else:
for i in range(i):
if not (i == 0):
if list1[i] != list2[i]:
print list1[i]
print list2[i]
Is there a better way to do this? (Python 2.x)
list1=[1,2,3,4]
list2=[1,5,3,4]
print [(i,j) for i,j in zip(list1,list2) if i!=j]
Output:
[(2, 5)]
Edit: Easily extended to skip n first items (same output):
list1=[1,2,3,4]
list2=[2,5,3,4]
print [(i,j) for i,j in zip(list1,list2)[1:] if i!=j]
Nobody's mentioned filter:
a = [1, 2, 3]
b = [42, 3, 4]
aToCompare = a[1:]
bToCompare = b[1:]
c = filter( lambda x: (not(x in aToCompare)), bToCompare)
print c
There's a nice class called difflib.SequenceMatcher
in the standard library for that.
edit: oops, didn't see the "ignore first item" part
from itertools import islice,izip
for a,b in islice(izip(list1,list2),1,None):
if a != b:
print a, b
Noting the requirement to skip the first line:
from itertools import izip
both = izip(list1,list2)
both.next() #skip the first
for p in (p for p in both if p[0]!=p[1]):
print pair
- This uses
izip
, an iterator (itertools) version ofzip
, to generate an iterator through pairs of values. This way you don't use up a load of memory generating a complete zipped list. - It steps the
both
iterator by one to avoid processing the first item, and to avoid having to make the index comparison on every step through the loop. It also makes it cleaner to read. - Finally it steps through each tuple returned from a generator which yields only unequal pairs.
You could use sets:
>>> list1=[1,2,3,4]
>>> list2=[1,5,3,4]
>>> set(list1[1:]).symmetric_difference(list2[1:])
set([2, 5])
You can use set operation
to find Symmetric difference (^) between two lists. This is one of the best pythonic ways to do this.
list1=[1,2,3,4]
list2=[1,5,3,4]
print(set(list1) ^ set(list2))
So the output will be {2, 5}
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