纯JavaScript逻辑小结

 

1.二维数组变为一维数组

 

function double_to_one() {
 
  collection = [1,[2],[3,4]]
  var array  = [];
  for(var i = 0;i< collection.length;i++){
      var new_array = collection[i];
     if( new_array instanceof Array == true ){
        for(var j = 0;j< new_array.length;j++){
           array.push(new_array[j]);
         }
    }
    else{
      array.push(new_array);
    }
 }
  return array;
}
// array = [1,2,3,4]

 2.数组排序

从大到小
var rank_asc = function(){
     var collection = [2,4,1,6,5,3]
     var array = collection.sort();
      array = array.reverse();
  return array;
};
//array = [6,5,4,3,2,1]
从小到大
var rank_asc = function(collection){
   var collection = [1,4,2,6,3,5]
     var array = collection.sort();
  return array;
};
// array = [1,2,3,4,5,6]

 3,给出的数组，按照给定结果输出

 

function count_same_elements_3(collection){
  var collection = var collection = [
    "a", "a", "a",
    "e", "e", "e", "e", "e", "e", "e",
    "h", "h", "h", "h", "h", "h", "h[3]", "h", "h",
    "t", "t-2", "t", "t", "t", "t", "t", "t", "t[10]",
    "f", "f", "f", "f", "f", "f", "f", "f", "f",
    "c:8",
    "g", "g", "g", "g", "g", "g", "g",
    "b", "b", "b", "b", "b", "b",
    "d-5"
  ];
  var result = [];
  var new_array = [];
  var length = collection.length;
  for(var i = 0;i < length; i++){
    for(var j = i+1; j < length; j++){
      if(collection[i] === collection[j]){
        j = ++i;
      }
    }
    new_array.push(collection[i]);
  } // 去重复
  for(var i=0;i<new_array.length;i++){
    var number = 0;
    var temp = new_array[i];
    var position = temp.indexOf('-');// '-'存在位置
    var positions = temp.indexOf(':');
    var positionss = temp.indexOf('[');
    if(position != -1 ){         //-1就是表示有对应的特殊符号（‘-’）
       number = parseFloat(temp.substr(position + 1));//截取字符串 
       temp = temp.substr(0,position);
    }
    else if(positions != -1){
       number = parseFloat(temp.substr(positions + 1));
       temp = temp.substr(0,positions);
    }
    else if(positionss != -1){
       number =  parseFloat(temp.substr(positionss + 1));
       temp = temp.substr(0,positionss);
    }
    else{
      for(var j = 0; j < collection.length; j++){
        if(collection[j] == temp){
          number++;
        }
      }
    }
    var k = {name: temp, summary: number};
    if(result.length == 0){
      result.push(k);
    }
    else {
      for (var n = 0, len = result.length; n < len; n++) {
        if (k.name == result[n].name) {
          result[n].summary += k.summary;
        }
        else if(k.name !== result[n].name && n == len -1){   //这是直到数组的最后一个
          result.push(k);
        }
      }
    }
    number = 0;
  }
  return result;
}

//   预先给定的输出结果  result = [
      {name: "a", summary: 3},
      {name: "e", summary: 7},
      {name: "h", summary: 11},
      {name: "t", summary: 19},
      {name: "f", summary: 9},
      {name: "c", summary: 8},
      {name: "g", summary: 7},
      {name: "b", summary: 6},
      {name: "d", summary: 5}
]

 4.小数取整

 

1.丢弃小数部分,保留整数部分 

parseInt(5/2) // 2 
parseInt(7/4) //1 

2.向上取整,有小数就整数部分加1 

Math.cell(5/3) // 2
Math.ceil(5/2) //3 

3,四舍五入. 
Math.round(5/2)  //3

4,向下取整 
Math.floor(5/3) //1
 Math.floor(5/2) //2