contains, distinct, group by, select many

contains.js

Array.prototype.contains = function(value, comparison){
    comparison = comparison || function(A,B){
        return (A === B);
    };
    
    return this.some(function(item){
        return comparison(item, value);
    });
};

distinct.js

function distinct(arr, comparison){
    var acc = [];
    for(var i = 0; i<arr.length; i++){
        if(!acc.contains(arr[i], comparison)){
            acc.push(arr[i]);
        }
    }
    return acc;
}

distinctFast.js

Array.prototype.distinct = function(comparison){
    if(comparison) return distinct(this, comparison);
    var set = {};
    var acc = [];
    for(var i = 0; i<arr.length; i++){
        if(!set[arr[i]]){
            set[arr[i]] = true;
            acc.push(arr[i]);
        }
    }
    return acc;
};

flatten.js

function flatten(array){
    if(typeof array.selectMany === 'function'){
        return array.selectMany(flatten);
    } else {
        return [array];
    }
}

selectmany.js

Array.prototype.selectMany = function(selector){
    selector = selector || function(value){return value;};
    var acc = [];
    var mapped = this.map(selector);
    for(var i = 0; i<mapped.length; i++){
        for(var j = 0; j<mapped[i].length; j++){
            acc.push(mapped[i][j]);
        }
    }
    return acc;
};