circular numpy array indices

Question

I have a 1-D numpy array a = [1,2,3,4,5,6] and a function that gets two inputs, starting_index and ending_index, and returns a[stari

Answer 1

np.take has a wrap mode:

In [171]: np.take(np.arange(1,7),range(4,7),mode='wrap')
Out[171]: array([5, 6, 1])

That's not quite what you want.

Actually, modulus does the same thing

In [177]: a[np.array([4,5,6])%6]
Out[177]: array([5, 6, 1])

But how about a small function that turns (4,1) into [4, 5, 6], or if you prefer [4, 5, 0]?

def foo(a, start, stop): 
    # fn to convert your start stop to a wrapped range
    if stop<=start:
        stop += len(a)
    return np.arange(start, stop)%len(a)

a[foo(a,4,1)]  # or
np.take(a,foo(a,4,1))