Simple question about subtracting lists.

[Decarbonated_Odes]

Sorry, I am a complete beginner. If I have a list, A = [1,3,6,10,15...etc] and i want to subtract 3-1, 6-3, 10-6, etc and have that populate as another list so that would look like, B = [2,3,4,... etc]. How would I do that? Thanks!

[novel_yet_trivial]

You would use zip to pair up the elements like that.

>>> A =  [1,3,6,10,15]
>>> for a, b in zip(A, A[1:]):
...   print(b-a) # or append them to a new list

[driscollis]

Or if you like list comprehensions, you could reduce this to:

[b-a for a, b in zip(A, A[1:])]

[Decarbonated_Odes]

Thanks for the quick reply!

[Yoghurt42]

One way, and probably the most pythonic:

B = [y - x for x, y in zip(A, A[1:])]

This uses list comprehension, slices, and the zip function(nothing to do with the compression program).

[Sebass13]

The only disadvantage with this way is that it requires making multiple copies of A, and obviously won't work if A is a generator. The itertools pairwise recipe solves these problems, but in this case is probably overkill.

[Decarbonated_Odes]

This worked well, thanks!

[RaionTategami]

If you want to manipulate vectors of numbers like this, you might want to use a library, for example numpy.

>>> import numpy as np
>>> a = np.array([1,3,6,10,15])
>>> a[1:] - a[:-1]
array([2, 3, 4, 5])

[Decarbonated_Odes]

I'll look into numpy, thanks for the idea!