CODEWITHSUNDEEP
pythonlistpython-3.x
misheekoh
misheekoh

Reputation: 460

Traversing through a list while comparing 2 elements

I'm relatively new to python and programming, I am trying to solve a problem which requires to print out the pair of numbers where the difference of both numbers == 2. Here's my attempt:

l = [1, 2, 3, 5, 7, 11, 13, 17, 19, 23]
    k = []
    count = 0                  
    a = l[0]              #initialize a to be the element in the first index
   #b = l[1]
        while (count < len(l)):       #while count is less than length of list
            for i in range(len(l)):    #for each element i in l,
                k.append(a)            #append it to a new list k
                a, b = l[i+1], l[i+1]  #Now a and b pointers move to the right by 1 unit
                count += 1             #update the count
            print(k[i])            #print newly updated list k

       if(a - b == 2):       #attempting to get the difference of 2 from a,b. if difference a,b == 2, append them both
                             #If fail, move on to check the next 2 elements.
           #k.append(l[i])

print(k)

The code gets stuck at a,b = l[i+1],l[i+1]. To help you visualize what's going on with the code, refer to: http://goo.gl/3As1bD

Appreciate any help! Sorry if it's abit messy. All I want to do is to be able to traverse each element in the list while comparing their differences if it's == 2

Thanks! Looking forward to alternatives

Upvotes: 0

Views: 57

Answers (3)

Kasravnd
Kasravnd

Reputation: 107337

The problem is that you are iterating over range(len(l)) and tried to get the front item by l[i+1] which makes you get an IndexError:

For example :

>>> l = [1,2,3]
>>> 
>>> l[len(l)+1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list index out of range

For get ride of this problem you should loop over range(len(l)-1) and for first item use l[i]: 

for i in range(len(l)-1):    #for each element i in l,
                k.append(a)            #append it to a new list k
                a, b = l[i], l[i+1]

Upvotes: 2

Martin Konecny
Martin Konecny

Reputation: 59661

Why not do a double nested for loop:

l = [1, 2, 3, 5, 7, 11, 13, 17, 19, 23]
for i in l:
    for j in l:
        if abs(i-j) == 2:
            print(i, j)

Upvotes: 0

vks
vks

Reputation: 67978

You can simply do

l = [1, 2, 3, 5, 7, 11, 13, 17, 19, 23]
[(i,j) for i,j in zip(l,l[1:]) if abs(i-j)==2]

Output:[(3, 5), (5, 7), (11, 13), (17, 19)]

Upvotes: 2

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