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    ndarray-select

    1.0.1 • Public • Published

    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.

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    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 ndarray
    • k is the rank of the item which is being selected
    • compare 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 ndarray
    • useCompare is a flag which if set uses a comparison function
    • dtype is the datatype of the array

    Returns An optimized ndselect function

    License

    (c) 2014 Mikola Lysenko. MIT License

    Install

    npm i ndarray-select

    DownloadsWeekly Downloads

    606

    Version

    1.0.1

    License

    MIT

    Last publish

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