Index Entire Array Backwards In For Loop

Suppose I would like to loop over an array and within the loop index the array forward and backward for all of its indices like so: x = np.random.uniform(size=600) for i in range(l

Solution 1:

Use an end of slice value of -i or None. If i is non-zero, then it's just -i, but if it's 0, then -0 is falsy, and it evaluates and returns the second term, None, which means "run to end of sequence". This works because foo[:None] is equivalent to foo[:], when you omit that component of the slice it becomes None implicitly, but it's perfectly legal to pass None explicitly, with the same effect.

So your new line would be:

dot = np.dot(x[:-i or None], x[i:])

Solution 2:

Why don't you just use the length information:

length = len(x)

for i in range(length):
    dot = np.dot(x[:length-i], x[i:])