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如何在javascript中统计数组中重复的值

javascriptarrays
183

目前，我有一个数组如下:

var uniqueCount = Array();

几步之后，我的数组看起来像这样：

uniqueCount = [a,b,c,d,d,e,a,b,c,f,g,h,h,h,e,a];
我该如何计算数组中有多少个a、b、c？我希望得到这样的结果：
a = 3
b = 1
c = 2
d = 2
1
可能是 https://dev59.com/DGnWa4cB1Zd3GeqPykA9 的重复问题。 - Vinay Pratap Singh Bhadauria
@Nirk 我猜musical_coder指的是{}这种类型的map，而不是函数式编程中的map。 - Matt Ball
35个回答
0

最快的方法：

计算复杂度为O(n)。

function howMuchIsRepeated_es5(arr) {
 const count = {};
 for (let i = 0; i < arr.length; i++) {
  const val = arr[i];
  if (val in count) {
   count[val] = count[val] + 1;
  } else {
   count[val] = 1;
  }
 }

 for (let key in count) {
  console.log("Value " + key + " is repeated " + count[key] + " times");
 }
}

howMuchIsRepeated_es5(['a','b','c','d','d','e','a','b','c','f','g','h','h','h','e','a']);

最短的代码：

使用ES6。

function howMuchIsRepeated_es6(arr) {
 // count is [ [valX, count], [valY, count], [valZ, count]... ];
 const count = [...new Set(arr)].map(val => [val, arr.join("").split(val).length - 1]);

 for (let i = 0; i < count.length; i++) {
  console.log(`Value ${count[i][0]} is repeated ${count[i][1]} times`);
 }
}

howMuchIsRepeated_es6(['a','b','c','d','d','e','a','b','c','f','g','h','h','h','e','a']);

0

返回字符串中最常用的字符的示例。

function maxChar(str) {
    const charMap = {};

    let maxCharacter = '';
    let maxNumber = 0;

    for (let item of str) {
        charMap[item] = charMap[item] + 1 || 1;
    }

    for (let char in charMap) {
        if (charMap[char] > maxNumber) {
            maxNumber = charMap[char];
            maxCharacter = char;
        }
    }

    return maxCharacter;
}


console.log(maxChar('abcccccccd'))

0

var string = ['a','a','b','c','c','c','c','c','a','a','a'];

function stringCompress(string){

var obj = {},str = "";
string.forEach(function(i) { 
  obj[i] = (obj[i]||0) + 1;
});

for(var key in obj){
  str += (key+obj[key]);
}
  console.log(obj);
  console.log(str);
}stringCompress(string)

/*
Always open to improvement ,please share 
*/

0
var arr = ['a','d','r','a','a','f','d'];  

//call function and pass your array, function will return an object with array values as keys and their count as the key values.
duplicatesArr(arr);

function duplicatesArr(arr){
    var obj = {}
    for(var i = 0; i < arr.length; i++){
        obj[arr[i]] = [];
        for(var x = 0; x < arr.length; x++){
            (arr[i] == arr[x]) ? obj[arr[i]].push(x) : '';
        }
        obj[arr[i]] = obj[arr[i]].length;
    }

    console.log(obj);
    return obj;
}
-1
public class CalculateCount {
public static void main(String[] args) {
    int a[] = {1,2,1,1,5,4,3,2,2,1,4,4,5,3,4,5,4};
    Arrays.sort(a);
    int count=1;
    int i;
    for(i=0;i<a.length-1;i++){
        if(a[i]!=a[i+1]){
            System.out.println("The Number "+a[i]+" appears "+count+" times");
            count=1;                
        }
        else{
            count++;
        }
    }
    System.out.println("The Number "+a[i]+" appears "+count+" times");

}

}

你能为这个添加一些上下文吗？ - Neo
这是关于 JavaScript，而不是 Java。 - Reza Saadati
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