使用javascript/jquery从现有数组中创建一个新数组，该数组保存项目存在的次数

Create a new array from an existing array that holds the count for how many times an item exist using javascript/jquery

本文关键字：数组 新数组 保存 存在 项目 一个 jquery javascript 创建 使用      更新时间：2023-09-26

我有一个数组中的项列表，我想创建一个新数组，它是一个对象数组，键是现有数组中的值，值是该项在现有数组中出现的次数。希望从那以后，如果不希望这个例子会有所帮助的话。请不要使用像lodash或下划线这样的第三方库。

如有任何帮助，我们将不胜感激，谢谢。

var arr = [a,a,a,b,c,c,d,e,f,f,f,f];
new array =[{a:3},{b:1},{c:2},{d:1},{e:1},{f:4}];

到目前为止我的尝试：

            countryCodes.sort();
            var result = count(countryCodes);
            console.log(result[0]+": "+result[1]);
            function count(arr) {
                var a = [], b = [], prev;
                arr.sort();
                for ( var i = 0; i < arr.length; i++ ) {
                    if ( arr[i] !== prev ) {
                        a.push(arr[i]);
                        b.push(1);
                    } else {
                        b[b.length-1]++;
                    }
                    prev = arr[i];
                }
                return [a, b];
            }

你很接近。

var a = "aa",
    b = "bb",
    c = "cc",
    d = "dd",
    e = "ee",
    f = "ff";
var arr = [a,a,a,b,c,c,d,e,f,f,f,f];
function getCount(arr) {
  var result = {};
  
  for (var val of arr) result[val] = result[val] + 1 || 1;
  
  return result;
}
var totals = getCount(arr);
document.write(JSON.stringify(totals));

按下run按钮时打开console。

var arr = ['a', 'a', 'a', 'b', 'c', 'c', 'd', 'e', 'f', 'f', 'f', 'f'];
function getObjectFromArray(a) {
  var result = [],
      alreadyAdded = [];
  a.forEach(function(item) {
    var key = item,
      obj = {};
    if (alreadyAdded.indexOf(item) != -1) return;
    alreadyAdded.push(item)
    obj[key] = getCount(a, item)
    result.push(obj)
  })
  return result;
}
function getCount(a, el) {
  var count = 0;
  a.forEach(function(element) {
    if (element == el) count++
  })
  return count;
}
console.log(getObjectFromArray(arr))

这里是另一种工作方式。

   function count(arr) {
    var prev = arr[0];
    var current;
    var newArr = [];
    var count = 0;
    var obj = {};
    for (var i = 0; i < arr.length; i++) {
        current = arr[i];
        if (i == arr.length - 1) {
            if (prev == current) { 
                count++;
                obj = {};
                obj[prev] = count;
                newArr.push(obj);
            }
            else {
                obj = {};
                obj[prev] = count;
                newArr.push(obj);
                count = 1;
                obj = {};
                obj[current] = count;
                newArr.push(obj);
            }
        }
        else if (prev == current) {
            count++;
        }
        else {
            obj = {};
            obj[prev] = count;
            newArr.push(obj);
            count = 1;
            prev = current;
        }
    }
    return newArr;
}
        console.log(count(['a', 'a', 'a', 'b', 'c', 'c', 'd', 'e', 'f', 'f', 'f', 'f']));

使用Array.prototype.reduce() 这可能是一项非常简单的任务

var arr = ["a","a","a","b","c","c","d","e","f","f","f","f"],
    res = arr.reduce((p,c) => { var i = p.findIndex(e => !!e[c]);
                                !!~i ? p[i][c]++ : p.push({[c]:1});
                                return p},[]);
document.write("<pre>" + JSON.stringify(res) + "</pre>");

下面这个应该像o（2n）一样快，它只不过是两行对象赋值。

var arr = ["a","a","a","b","c","c","d","e","f","f","f","f"],
    mid = arr.reduce((p,c) => {!!p[c] ? p[c]++ : p[c]=1; return p},{}),
    res = Object.keys(mid).map(e => ({[e]:mid[e]}));
document.write("<pre>" + JSON.stringify(res) + "</pre>");

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