[Numpy-discussion] howto exclude elements from sorted array which are present in other sorted array

[Charles R Harris]

On 5/29/07, dmitrey <openopt at ukr.net> wrote:
>
> hi all,
> I have 2 sorted arrays arr1 & arr2 (ascending order, for example
> [1,2,5,8] and [3,5], but length may be thousands, so I need simpliest
> way, not costly).
> Howto obtain arr3 that consists of elements present in arr1 but absent
> in arr2?
> Of course, I can write something by myself, like
> arr3 = [x for x in arr1 if not x in arr2]
> but maybe already written routines are present in numpy? (that use sort)
>
> Usually arr2 is much more small than arr1, typical former size is 10-20
> and typical latter size can be 1000-10000



count = arr2.searchsorted(arr1, side='right') - arr2.searchsorted(arr1,
side='left')
arr3 = arr1[count == 0]

Chuck
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