CODEWITHSUNDEEP
python
Patrick Weiß
Patrick Weiß

Reputation: 456

Check if a list contains incrementing elements starting from zero

I want to check if a list contains incrementing elements, incremented by one each and starting with 0. So, e.g. [0, 1, 2, 3] should return "valid", whereas e.g. [0, 1, 3, 4] or [-1, 0, 1] should return "not valid".

Is there an easy way to achieve that in Python? Maybe a built-in function?

Upvotes: 1

Views: 4391

Answers (3)

Radek Hofman
Radek Hofman

Reputation: 527

I think it can be solved via a one-liner in a functional manner:

print not len(filter(lambda i: i!=-1, [x[i]-x[i+1] for i in range(len(x)-1)]))

given True for x = [0, 1, 2, 3] and False for x = [0, 1, 3, 4]

Explanation:

 [x[i]-x[i+1] for i in range(len(x)-1)]

makes a list of differences between successive elements, obviously we want to have all -1...

Then we use filter to select those elements which are different from -1, if there is at least one, it is not a incrementing elements and so the length of such filtered list > 0

If yes, i.e. there are just -1, the field is empty and we get length of 0.

Upvotes: 1

Iron Fist
Iron Fist

Reputation: 10951

How about using all :

>>> l = [0, 1, 2, 3]
>>> not l[0] and all(y-x==1 for x,y in zip(l, l[1:]))
True
>>> l1 = [0,1,2,3,5,7]
>>> not l[0] and all(y-x==1 for x,y in zip(l1, l1[1:]))
False
>>> l2 = [0,1,2,3,4,7]
>>> not l[0] and all(y-x==1 for x,y in zip(l2, l2[1:]))
False
>>> l3=[-1,0,1,2]
>>> not l[0] and all(y-x==1 for x,y in zip(l3, l3[1:]))
False
>>> l2 = [0,1,2,3,4,5,7]
>>> not l[0] and all(y-x==1 for x,y in zip(l2, l2[1:]))
False
>>> l4=[0,2,3,4,5,7,8]
>>> not l[0] and all(y-x==1 for x,y in zip(l4, l4[1:]))
False
>>> l5=[0,2,3,4,5,6,7,8]
>>> not l[0] and all(y-x==1 for x,y in zip(l5, l5[1:]))
False

So you can put this into a function, this way:

def check_my_list(lst):
    if not lst:
        print 'List Empty'
        return False
    test = not lst[0] and all(y-x==1 for x,y in zip(lst,lst[1:])
    return test

Upvotes: 3

Nelewout
Nelewout

Reputation: 6564

If the problem is truly as you describe it, this can be solved trivially using range, like so:

myList = [...]
if myList == list(range(myList[-1] + 1)):
    # Do stuff.

Upvotes: 12

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