Count how many identical elements in 2 arrays occur

I have a form and as a result of that form I have two arrays - one for personA's details and one for personB's details. One part of the form is a bunch of checkboxes of dates - th开发者_高级运维e dates are a fixed price, but booking for two on the same date is a reduced price.

What I want to do is compare personA's array with personB's array and for any duplicates issue a reduced rate.

The rate will be calculated into two variables - total full price dates (in £s) and total reduced price dates (in £s).

Here is my code so far (this occurs on the checkboxes onclick):

function processDates(){
    var contentsA, valsA = [], dates_A =  document.forms['registerForm']['personADates[]'];
    for(var iA=0,elmA;elmA = dates_A[iA];iA++) {
        if(elmA.checked) {
            valsA.push(elmA.value);
        }
    }
    contentsA = valsA.join(', ');

    var contentsB, valsB = [], dates_B =  document.forms['registerForm']['personBDates[]'];
    for(var iB=0,elmB;elmB = dates_B[iB];iB++) {
        if(elmB.checked) {
            valsB.push(elmB.value);
        }
    }
    contentsB = valsB.join(', ');
}

• With my own http://phrogz.net/JS/ArraySetMath.js you could do:

  // If the original order of the elements is not important
  var common = array1.intersect( array2 );
  
  // If the original order of the elements is important
  var common = array1.unsortedIntersect( array2 );
  

• With the larger JS.Set you could do:

  // If the original order of the elements is not important
  var common = (new JS.SortedSet(array1)).intersect(new JS.SortedSet(array2));
  
  // If the original order of the elements is important
  var common = (new JS.Set(array1)).intersect(new JS.Set(array2));
  

It is not clear to me what the values in your arrays actually are; are these dates entered by the user in plain text? If so, you'll want to ensure that they are normalized so that they are comparable and guaranteed to match.

If these are more than simple comparable objects (e.g. instead of String or Date instances you are creating arrays complex Objects) then my library allows you to supply a comparison function so you can determine which are equal. See the library for more details on this.

Instead of using an array you could use an object (warning... untested code):

function processDates(){
    var valsA = {}, dates_A =  document.forms['registerForm']['personADates[]'];
    for(var iA=0,elmA;elmA = dates_A[iA];iA++) {
        if(elmA.checked) {
            valsA[elmA.value] = 1;  // Store values
        }
    }

    var samedate = [];
    var dates_B = document.forms['registerForm']['personBDates[]'];
    for(var iB=0,elmB;elmB = dates_B[iB];iB++) {
        if(elmB.checked) {
            if (valsB[elmB.value])
            {
                // Here we found a date that's present in both
                samedate.push(elmB.value);
            }
        }
    }
    // Here samedate is a list of all dates listed in both A and B
}

If functional javascript is an option:

_.sum = function(array) {
    return _.reduce(array, function(memo, val) {
        return memo + val;
    }, 0);
};

var duplicates = _.intersect(valsA, valsB);
var fullPrice = _.sum(valsA.concat(valsB));
var reducedPrice = fullPrice - discountScalar * _.sum(duplicates);

Relies on underscore.js for easy cross browser implentation of functional methods. Most of these can be implemented with array.reduce & array.map on modern browsers.