Check if there is a number near the same number in a list - python

Question

I want to check if for example the int 2 comes after or before another 2:

list = [2, 2, 3]
if 2 and 2 in list:
    print "True"

And if the list is this:

list = [2, 3, 2]
print "False"

thx

What have you attempted? And what exactly is the problem - you are checking whether there are two of some input number beside one another in a list? — miradulo, Feb 04 '17 at 16:26
yes I am checking if there are two of some input number beside one another in a list. — Telep0rter, Feb 04 '17 at 16:28
State problem statement. Nobody is getting what you want to ask. New to python is a excuse but I hope you know how to code! — Pbd, Feb 04 '17 at 16:28
@Telep0rter you can [enumerate](http://stackoverflow.com/a/126533/2102114) a list to obtain index, item and then check if `list[index] == list[index+1]` — S Raghav, Feb 04 '17 at 16:29
you need only scan the list in a loop, such as for i in range(len(list)-1): if list[i] == list[i+1]: found=True; break; then outside the loop, you check if found is true. of course you need to initiate found to be False before the loop. — Shiping, Feb 04 '17 at 16:32

score 1 · Accepted Answer · answered Feb 04 '17 at 16:49

1

Try this:

def check(list_):
    last = None
        for element in list_:
            if element == last:
                return True
            else:
                last = element
    return False

answered Feb 04 '17 at 16:49

Batman

8,571
7
41
80

wwii · Answer 2 · 2017-02-04T17:05:45.723

a = [0, 2, 15, 13, 13, 5, 12, 3, 1, 3, 14, 14, 17, 20, 0, 14, 2, 0,
     1, 10, 5, 13, 15, 13, 19, 11, 20, 5, 4, 17, 20, 7, 4, 20, 20,
     19, 3, 20, 20, 0, 14, 8, 18, 0, 18, 2, 5, 15, 12, 20, 5, 7, 12,
     6, 17, 18, 15, 12, 2, 16, 6, 11, 14, 20, 8, 4, 11, 10, 15, 6,
     10, 19, 1, 20, 6, 19, 2, 5, 13, 7, 5, 18, 11, 11, 3, 0, 11, 3,
     14, 18, 15, 11, 2, 9, 12, 0, 18, 1, 4, 2]

Run through the list once to find all the pairs and put them in a set

z = {x for x, y in zip(a, a[1:]) if x == y}

>>> z
{11, 20, 13, 14}

Then use it like this:

>>> n = 2
>>> n in z
False
>>> n = 13
>>> n in z
True
>>>

zip(a, a[1:])

will produce tuples of (a[0], a[1]), (a[1], a[2]), (a[2], a[3]), ...

The pairwise Itertools Recipe will do the same thing.

Check if there is a number near the same number in a list - python

2 Answers2