countFrequency.js

/**
 * This function searches an array and its sub-arrays. A condition function can be used
 * to limit the results
 * @param {Array} arr
 * @param {Function} condfn A function with extra conditions
 * @param {String} prop A hashable property to identify the object when found
 * @param {Object} c A collector object defined by the function
 * @returns {Object} An object containing the found objects
 */
function countFrequency(arr, condfn, prop, c) {
    c = c || {
        items: {},//items to be returned
        add: function(item, cond) {
            var hash = prop !== undefined ? item[prop] : item;
            if(cond) { //if the condition test true
                //if no item was found then add it
                if(!this.items[hash]) this.items[hash] = 1;
                //otherwise increment the counter
                else this.items[hash]++;
            }
        }
    };
    
    var l = arr.length;
    for(var i=0; i<l; i++) {
        var item = arr[i]; //the current item
        //call the function recursively with the branch-array
        if(item instanceof Array) searchArray(item, condfn, prop, c);
        else {
            //test to see if the object meet the criteria. If not function is
            //found the set to true
            var cond = condfn ? condfn.call(undefined, item) : true;
            c.add(item, cond);
        }
    }
    
    return c.items; //done
}

/*====================EXAMPLES =====================*/

var a = [9,8,9,[6,1,[2,9]]];
console.log(searchArray(a));
//result: { '1': 1, '2': 1, '6': 1, '8': 1, '9': 3 }

var b = [9,8,9,[6,1,[2,9]]];
console.log(searchArray(b, function(item){ return item % 3 === 0; }));
//result: { '6': 1, '9': 3 }

var c = [['frank', 'arthur'],'annie', 'bruce', 'anthon',['simone', 'andrew']];
console.log(searchArray(c, function(name){return name.charAt(0) === 'a'; }));
//result: { arthur: 1, annie: 1, anthon: 1, andrew: 1 }