Question

我有一个数组中的项目列表，我想创建一个新数组，该数组是一个对象数组，其中键是现有数组的值，值是该项目在现有数据中的次数阵列。希望这样做，如果没有希望这个例子会有所帮助。没有像lodash或下划线那样的第三方图书馆。

非常感谢任何帮助，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];
            }

Answer 1

你很亲密。

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));

Answer 2

按console按钮时打开run。

＆＃13;

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))

＆＃13;

Answer 3

这是另一种工作方式。

   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']));

Answer 4

使用Array.prototype.reduce()

这可能是一项非常简单的任务

＆＃13;

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>");

＆＃13;

好的，下面的一个应该像o（2n）一样快，并且它不会比两行对象分配更长。

＆＃13;

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>");

＆＃13;

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

4 个答案: