Finding Matching And Nonmatching Items In Lists

I'm pretty new to Python and am getting a little confused as to what you can and can't do with lists. I have two lists that I want to compare and return matching and nonmatching el

Solution 1:

Use set instead of list. This way you can do lots of nice things:

set1 = set(['dog', 'cat', 'pig', 'donkey'])
set2 = set(['dog', 'cat', 'donkey'])

matched = set1.intersection(set2) # set(['dog', 'cat', 'donkey'])unmatched = set1.symmetric_difference(set2) # set(['pig'])

I know it's not exactly what you asked for, but it's usually a better practice to use sets instead of lists when doing this sort of things.

More on sets here: http://docs.python.org/library/stdtypes.html#set

Solution 2:

use the following code.

listt3=[]

for i in listt1:
    if i in listt2:
        listt3.append(1)
    else:
        listt3.append(0)

If you prefer one-liners,

listt3=[ 1 if i in listt2 else 0 for i in listt1]

Solution 3:

Here is how I would do it if list2 is short:

list1 = ['dog', 'cat', 'pig', 'donkey']
list2 = ['dog', 'cat', 'donkey']
list3 = [int(val in list2) for val in list1]
print(list3)

This prints:

[1, 1, 0, 1]

If list2 is long, you could convert it to a set first to make the code more efficient:

list1 = ['dog', 'cat', 'pig', 'donkey']
set2 = set(['dog', 'cat', 'donkey'])
list3 = [int(valin set2) forvalin list1]
print(list3)

The reason your current code produces too many elements is that you call append() on every iteration of the inner loop, and there are len(List1) * len(List2) such iterations.

Here is how it can be fixed:

defmatch_nonmatch(List1, List2):
    List3 = []
    for i inrange(len(List1)):
        for j inrange(len(List2)):
            if List1[i] == List2[j]:
                List3.append(1)
                break# fix #1else:                     # fix #2
            List3.append(0)
    return List3

Note the added break and the fact that the else clause is now refers to the inner for and not the if.

That said, I'd still use the one-liner at the top of my answer.

Solution 4:

You can use bitwise operation too:

List1 = ['dog', 'cat', 'pig', 'donkey']  
List2 = ['dog', 'cat', 'donkey']  

matching:

set(List1) & set(List2)   

not matching:

set(List1) ^ set(List2) 

Solution 5:

>>> list1 = ['dog', 'cat', 'pig', 'donkey']; list2 = ['dog', 'cat', 'donkey']
>>> [i in list2 for i in list1]
[True, True, False, True]

Also, you should read PEP8, CamelCase names are commonly used for classes only.