qselect

QuickSelect.js

Implementation of the QuickSelect algorithm in Java for top-k computations

npm install

npm install qselect

code sample

  var QuickSelect = require('qselect');
 
  var array = [1,2,3,49,10,-1,-2]
 
    
 
  // QuickSelect rearranges the values so that the k smallest values occur in the first k positions
  // they are not necessarily in sorted order
 
  var cmp = function(a,b){return a<b;};
  var topk = QuickSelect(array,2,cmp).slice(0,2); 
  // should return an array containing the two smallest (-1, -2)
  
 
 
  var reversecmp = function(a,b){return a>b;};
  var topk = QuickSelect(array,2,reversecmp).slice(0,2); 
  // should return an array containing the two largest (10, 49)

When calling QuickSelect on an array larger than k, the value at index k after calling QuickSelect acts as a pivot. This means that no value with index less than k can be larger than the pivot, and no value with index larger than k can be smaller than the pivot.

Credit

Inspired by a code sample from Anno Langen.