根据underscore精简的函数（数组篇）

这里将underscore.js内的函数进行精简，指在帮助理解或者快速回忆起underscore.js的原理，更深入的了解函数式编程。

本文基于underscore.js1.8.3版本，参考手册为
http://www.css88.com/doc/underscore/

这里将精简underscore中提供的针对数组的操作，部分API已经在《根据underscore精简的函数（集合篇）》中体现，不再赘述。

_.initial

var initial = function (array, n) {    return Array.prototype.slice.call(array, 0, Math.max(0, array.length - (n == null ? 1 : n)));};var a =initial([5, 4, 3, 2, 1],2);console.log(a);

运行结果

[ 5, 4, 3 ]

_.rest

var rest=function(arr,n){    return Array.prototype.slice.call(arr,n==null?1:n);};var a =rest([5, 4, 3, 2, 1],2);console.log(a);

运行结果

[ 3, 2, 1 ]

_.first

var first=function(arr,n){    if(arr==null||arr.length<1) return void 0;    if(n==null) return arr[0];    return initial(arr,arr.length-n);};var a =first([5, 4, 3, 2, 1],2);console.log(a);

运行结果

[ 5, 4 ]

_.flatten

var isArray=function(obj){    return Object.prototype.toString.call(obj)==='[object Array]';};var flatte=function(input,shallow,strict,startIndex){    var output=[],idx=0;    for(var i=startIndex||0,length=input.length;i<length;i++){        var value=input[i];        if (isArray(value)){            if(!shallow) value=flatte(value,shallow,strict);            var j=0,len=value.length;            output.length+=len;            while(j<len){                output[idx++]=value[j++];            }        }else if(!strict){            output[idx++]=value;        }    }    return output;};var flatten = function (array, shallow) {    return flatte(array, shallow, false);};var a =flatten([1, [2], [3, [[4]]]]);var b =flatten([1, [2], [3, [[4]]]],true);console.log(a);console.log(b);

运行结果

[ 1, 2, 3, 4 ][ 1, 2, 3, [ [ 4 ] ] ]

_.uniq

var uniq=function(arr,isSorted){    var result=[],seen=[];    for(var i=0,length=arr.length;i<length;i++){        var value=arr[i],            computed=value;        if(isSorted){            if(!i||seen!==computed) result.push(value);            seen=computed;        }else if(result.indexOf(value)==-1){            result.push(value);        }    }    return result;};var a=uniq([1,1,1,1,2,2,2,3,3]);console.log(a);

运行结果

[ 1, 2, 3 ]

_.intersection

var intersection=function(array){    var result=[];    var argsLength=arguments.length;    for(var i=0,length=array.length;i<length;i++){        var item=array[i];        if (!(result.indexOf(item)==-1)) continue;        for(var j=1;j<argsLength;j++){            if(arguments[j].indexOf(item)==-1) break;        }        if(j===argsLength) result.push(item);    }    return result;};var a=intersection([1, 2, 3], [101, 2, 1, 10], [2, 1]);console.log(a);

运行结果

[ 1, 2 ]

_.difference

var difference = function(array) {    var rest = flatte(arguments, true, true, 1);    return filter(array, function(value){        return (rest.indexOf(value)==-1);    });};var a=difference([1, 2, 3, 4, 5], [5, 2, 10]);console.log(a);

运行结果

[ 1, 3, 4 ]

_.unzip

var unzip=function(array){    var length=array.length;    var result=Array(length);    for(var index=0;index<length;index++){        result[index]=_.pluck(array,index);    }    return result;};var names = ['moe', 'larry', 'curly'];var ages = [18, 23, 30];var sexes = ['male', 'female', 'male'];var students = unzip([names, ages, sexes]);console.log(students);

运行结果

[ [ 'moe', 18, 'male' ],  [ 'larry', 23, 'female' ],  [ 'curly', 30, 'male' ] ]

_.compact

var compact=function(array){    return filter(array,Boolean);};var a=compact([0, 1, false, 2, '', 3]);console.log(a);

运行结果

[ 1, 2, 3 ]

_.object

var object=function(list,values){    var result={};    for (var i=0,length=list.length;i<length;i++){        if(values){            result[list[i]]=values[i];        }else{            result[list[i][0]]=list[i][1];        }    }    return result;};var a=object(['moe', 'larry', 'curly'], [30, 40, 50]);var b=object([['moe', 30], ['larry', 40], ['curly', 50]]);console.log(a);console.log(b);

运行结果

{ moe: 30, larry: 40, curly: 50 }{ moe: 30, larry: 40, curly: 50 }

_.range

var range=function(start,stop,step){    if(stop==null){        stop=start||0;        start=0;    }    if(!step){        step=stop<start?-1:1;    }    var length=Math.max(Math.ceil((stop-start)/step),0);    var range=Array(length);    for(var idx=0;idx<length;idx++,start+=step){        range[idx]=start;    }    return range;};var a=range(0,30,5);console.log(a);

运行结果

[ 0, 5, 10, 15, 20, 25 ]

_.chunk

var chunk=function(arr,count){    if(count==null||count<1) return [];    var result=[];    var i=0,length=arr.length;    while(i<length){        result.push(Array.prototype.slice.call(arr,i,i+=count));    }    return result;};var a=chunk([1,2,3,4,5,6,7], 2);console.log(a);

运行结果

[ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ], [ 7 ] ]