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;ivar value=input[i];
if (isArray(value)){
if(!shallow) value=flatte(value,shallow,strict);
var j=0,len=value.length;
output.length+=len;
while(jelse 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;ivar 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;ivar item=array[i];
if (!(result.indexOf(item)==-1)) continue;
for(var j=1;jif(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;indexreturn 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;iif(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=stop1:1;
}
var length=Math.max(Math.ceil((stop-start)/step),0);
var range=Array(length);
for(var idx=0;idxreturn 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(iArray.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 ] ]