how does searchsort in python work?

python search sortedlist
Ars3nous picture Ars3nous · Mar 15, 2013 · Viewed 10.1k times · Source

To make my question clear say if I have an array a as Out[123]: [1, 3, 4, 6, 9, 10, 54] When I try to search the numbers in the list, searchsort returns correct value but when I try something not in the list, it returns an absurd value

here is some of the results

In [131]: a
Out[131]: [1, 3, 4, 6, 9, 10, 54]

In [132]: searchsorted(a,1)
Out[132]: 0

In [133]: searchsorted(a,6)
Out[133]: 3

In [134]: searchsorted(a,[9,54,1])
Out[134]: array([4, 6, 0])

In [135]: searchsorted(a,[9,54,1,0])
Out[135]: array([4, 6, 0, 0])
***> # here 0 is not in the list, but turns up @ position 0***

In [136]: searchsorted(a,740)
Out[136]: 7
***> # here 0 is not in the list, but turns up @ position 7***

why is this happening?

Answer

John Lyon picture John Lyon · Mar 15, 2013

searchsorted tells you where the element belongs to guarantee ordering:

Find the indices into a sorted array a such that, if the corresponding elements in v were inserted before the indices, the order of a would be preserved.

inserting 740 at position 7 would preserve ordering, as would inserting 0 at position 0.

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