[Numpy-discussion] all elements equal

[Neal Becker]

Keith Goodman wrote:

> On Mon, Mar 5, 2012 at 11:52 AM, Benjamin Root <ben.root@ou.edu> wrote:
>> Another issue to watch out for is if the array is empty.  Technically
>> speaking, that should be True, but some of the solutions offered so far
>> would fail in this case.
> 
> Good point.
> 
> For fun, here's the speed of a simple cython allclose:
> 
> I[2] a = np.ones(100000)
> I[3] timeit a.min() == a.max()
> 10000 loops, best of 3: 106 us per loop
> I[4] timeit allequal(a)
> 10000 loops, best of 3: 68.9 us per loop
> 
> I[5] a[1] = 9
> I[6] timeit a.min() == a.max()
> 10000 loops, best of 3: 102 us per loop
> I[7] timeit allequal(a)
> 1000000 loops, best of 3: 269 ns per loop
> 
> where
> 
> @cython.boundscheck(False)
> @cython.wraparound(False)
> def allequal(np.ndarray[np.float64_t, ndim=1] a):
>     cdef:
>         np.float64_t a0
>         Py_ssize_t i, n=a.size
>     a0 = a[0]
>     for i in range(n):
>         if a[i] != a0:
>             return False
>     return True

But doesn't this one fail on empty array?