ndarray-select
v1.0.1
Published
Linear time selection algorithm for ndarrays
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ndarray-select
Finds the kth element in an ndarray in linear time with high probability. This implementation is based on the quick select algorithm and mutates the array in place.
Examples
Single list
var pack = require("ndarray-pack")
var ndselect = require("ndarray-select")
var points = pack([0, 0, 1, 2.5, -1])
//Find the median element in the list
var median = ndselect(points, points.shape[0]>>1)
console.log(median.get())
Output
0 2.5 -1
Multiple lists
It is also possible to select vectors (using lexicographical comparisons):
var pack = require("ndarray-pack")
var ndselect = require("ndarray-select")
var points = pack([
[0, 0, 1],
[100, 0, 10],
[50, 1, 10],
[0, 2.5, -1],
[-1, -1, -1]
])
//Find the median element in the list
var median = ndselect(points, points.shape[0]>>1)
console.log(median.get(0), median.get(1), median.get(2))
Output
0 2.5 -1
Install
Install using npm:
npm install ndarray-select
API
var ndselect = require("ndarray-select")
ndselect(array, k[, compare])
Selects the kth item from the ndarray array
along the first axis of array
.
array
is an ndarrayk
is the rank of the item which is being selectedcompare
is an optional comparison function that gets a pair of ndarrays as input.
Returns An ndarray view of array.pick(k)
Note This method modifies array
. After completion, the element at position k
will be in sorted order, with all elements <array.pick(k)
occuring before k
and all elements >array.pick(k)
after k
in the list.
ndselect.compile(order, useCompare, dtype)
Precompiles an optimized selection algorithm for an array with the given index order and datatype.
order
is the order of the ndarrayuseCompare
is a flag which if set uses a comparison functiondtype
is the datatype of the array
Returns An optimized ndselect
function
License
(c) 2014 Mikola Lysenko. MIT License