Question

please tell me any good algorithm/code to get list of unique values from array and count of its occurrence in array. (i am using javascript).

Answer 1

For a method that will strip the duplicates from an array and returns a new array with the unique values, you may want to check the following Array.unique implementation. With an O(n²) complexity, it is certainly not the quickest algorithm, but will do the job for small unsorted arrays.

It is licensed under GPLv3, so I should be allowed to paste the implementation here:

// **************************************************************************
// Copyright 2007 - 2009 Tavs Dokkedahl
// Contact: http://www.jslab.dk/contact.php
//
// This file is part of the JSLab Standard Library (JSL) Program.
//
// JSL is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// any later version.
//
// JSL is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
// ***************************************************************************

Array.prototype.unique =
  function() {
    var a = [];
    var l = this.length;
    for(var i=0; i<l; i++) {
      for(var j=i+1; j<l; j++) { 
        if (this[i] === this[j])  // If this[i] is found later in the array
          j = ++i;
      }
      a.push(this[i]);
    }
    return a;
  };

You would be able to use it as follows:

var myArray = new Array("b", "c", "b", "a", "b", "g", "a", "b");
myArray.unique(); // returns: ["c", "g", "a", "b"]

You may want to tweak the above to somehow append the number of occurrences of each value.