How to count duplicate value in an array in javasc

问题:

Currently, I got an array like that:

var uniqueCount = Array();

After a few steps, my array looks like that:

uniqueCount = [a,b,c,d,d,e,a,b,c,f,g,h,h,h,e,a];

How can I count how many a,b,c are there in the array? I want to have a result like:

a = 3
b = 1
c = 2
d = 2

etc.

回答1:

function count() {
    array_elements = [\"a\", \"b\", \"c\", \"d\", \"e\", \"a\", \"b\", \"c\", \"f\", \"g\", \"h\", \"h\", \"h\", \"e\", \"a\"];

    array_elements.sort();

    var current = null;
    var cnt = 0;
    for (var i = 0; i < array_elements.length; i++) {
        if (array_elements[i] != current) {
            if (cnt > 0) {
                document.write(current + \' comes --> \' + cnt + \' times<br>\');
            }
            current = array_elements[i];
            cnt = 1;
        } else {
            cnt++;
        }
    }
    if (cnt > 0) {
        document.write(current + \' comes --> \' + cnt + \' times\');
    }

}

Demo Fiddle

回答2:

var counts = {};
your_array.forEach(function(x) { counts[x] = (counts[x] || 0)+1; });

回答3:

Something like this:

    uniqueCount = [\"a\",\"b\",\"c\",\"d\",\"d\",\"e\",\"a\",\"b\",\"c\",\"f\",\"g\",\"h\",\"h\",\"h\",\"e\",\"a\"];
    var  count = {};
    uniqueCount.forEach(function(i) { count[i] = (count[i]||0) + 1;});
    console.log(count);

Use a simple for loop instead of forEach if you don\'t want this to break in older browsers.

回答4:

I stumbled across this (very old) question. Interestingly the most obvious and elegant solution (imho) is missing: Array.prototype.reduce(...). All major browsers support this feature since about 2011 (IE) or even earlier (all others):

var arr = [\'a\',\'b\',\'c\',\'d\',\'d\',\'e\',\'a\',\'b\',\'c\',\'f\',\'g\',\'h\',\'h\',\'h\',\'e\',\'a\'];
var map = arr.reduce(function(prev, cur) {
  prev[cur] = (prev[cur] || 0) + 1;
  return prev;
}, {});

// map is an associative array mapping the elements to their frequency:
document.write(JSON.stringify(map));
// prints {\"a\": 3, \"b\": 2, \"c\": 2, \"d\": 2, \"e\": 2, \"f\": 1, \"g\": 1, \"h\": 3}

回答5:

Single line based on reduce array function

const uniqueCount =  [\"a\", \"b\", \"c\", \"d\", \"d\", \"e\", \"a\", \"b\", \"c\", \"f\", \"g\", \"h\", \"h\", \"h\", \"e\", \"a\"];
const distribution = uniqueCount.reduce((acum,cur) => Object.assign(acum,{[cur]: (acum[cur] | 0)+1}),{});
console.log(JSON.stringify(distribution,null,2));

回答6:

I think this is the simplest way how to count occurrences with same value in array.

var a = [true, false, false, false];
a.filter(function(value){
    return value === false;
}).length                                      

回答7:

You can solve it without using any for/while loops ou forEach.

function myCounter(inputWords) {        
    return inputWords.reduce( (countWords, word) => {
        countWords[word] = ++countWords[word] || 1;
        return countWords;
    }, {});
}

Hope it helps you!

回答8:

You can do something like that:

uniqueCount = [\'a\',\'b\',\'c\',\'d\',\'d\',\'e\',\'a\',\'b\',\'c\',\'f\',\'g\',\'h\',\'h\',\'h\',\'e\',\'a\'];
var map = new Object();

for(var i = 0; i < uniqueCount.length; i++) {
 if(map[uniqueCount[i]] != null) {
    map[uniqueCount[i]] += 1;
} else {
    map[uniqueCount[i]] = 1;
    }
}

now you have a map with all characters count

回答9:

You can have an object that contains counts. Walk over the list and increment the count for each element:

var counts = {};

uniqueCount.forEach(function(element) {
  counts[element] = (counts[element] || 0) + 1;
});

for (var element in counts) {
  console.log(element + \' = \' + counts[element]);
} 

回答10:

var uniqueCount = [\'a\',\'b\',\'c\',\'d\',\'d\',\'e\',\'a\',\'b\',\'c\',\'f\',\'g\',\'h\',\'h\',\'h\',\'e\',\'a\'];
// here we will collect only unique items from the array
var uniqueChars = [];

// iterate through each item of uniqueCount
for (i of uniqueCount) {
// if this is an item that was not earlier in uniqueCount, 
// put it into the uniqueChars array
  if (uniqueChars.indexOf(i) == -1) {
    uniqueChars.push(i);
  } 
}
// after iterating through all uniqueCount take each item in uniqueChars
// and compare it with each item in uniqueCount. If this uniqueChars item 
// corresponds to an item in uniqueCount, increase letterAccumulator by one.
for (x of uniqueChars) {
  let letterAccumulator = 0;
  for (i of uniqueCount) {
    if (i == x) {letterAccumulator++;}
  }
  console.log(`${x} = ${letterAccumulator}`);
}

回答11:

A combination of good answers:

var count = {};
var arr = [\'a\', \'b\', \'c\', \'d\', \'d\', \'e\', \'a\', \'b\', \'c\', \'f\', \'g\', \'h\', \'h\', \'h\', \'e\', \'a\'];
var iterator = function (element) {
    count[element] = (count[element] || 0) + 1;
}

if (arr.forEach) {
    arr.forEach(function (element) {
        iterator(element);
    });
} else {
    for (var i = 0; i < arr.length; i++) {
        iterator(arr[i]);
    }
}  

Hope it\'s helpful.

回答12:

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\");

}   

}

回答13:

Duplicates in an array containing alphabets:

var arr = [\"a\", \"b\", \"a\", \"z\", \"e\", \"a\", \"b\", \"f\", \"d\", \"f\"],
  sortedArr = [],
  count = 1;

sortedArr = arr.sort();

for (var i = 0; i < sortedArr.length; i = i + count) {
  count = 1;
  for (var j = i + 1; j < sortedArr.length; j++) {
    if (sortedArr[i] === sortedArr[j])
      count++;
  }
  document.write(sortedArr[i] + \" = \" + count + \"<br>\");
}

Duplicates in an array containing numbers:

var arr = [2, 1, 3, 2, 8, 9, 1, 3, 1, 1, 1, 2, 24, 25, 67, 10, 54, 2, 1, 9, 8, 1],
  sortedArr = [],
  count = 1;
sortedArr = arr.sort(function(a, b) {
  return a - b
});
for (var i = 0; i < sortedArr.length; i = i + count) {
  count = 1;
  for (var j = i + 1; j < sortedArr.length; j++) {
    if (sortedArr[i] === sortedArr[j])
      count++;
  }
  document.write(sortedArr[i] + \" = \" + count + \"<br>\");
}

回答14:

By using array.map we can reduce the loop, see this on jsfiddle

function Check(){
    var arr = Array.prototype.slice.call(arguments);
    var result = [];
    for(i=0; i< arr.length; i++){
        var duplicate = 0;
        var val = arr[i];
        arr.map(function(x){
            if(val === x) duplicate++;
        })
        result.push(duplicate>= 2);
    }
    return result;
}

To Test:

var test = new Check(1,2,1,4,1);
console.log(test);

回答15:

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 
*/

回答16:

Create a file for example demo.js and run it in console with node demo.js and you will get occurrence of elements in the form of matrix.

var multipleDuplicateArr = Array(10).fill(0).map(()=>{return Math.floor(Math.random() * Math.floor(9))});
console.log(multipleDuplicateArr);

var resultArr = Array(Array(\'KEYS\',\'OCCURRENCE\'));

for (var i = 0; i < multipleDuplicateArr.length; i++) {
  var flag = true;
  for (var j = 0; j < resultArr.length; j++) {
     if(resultArr[j][0] == multipleDuplicateArr[i]){
       resultArr[j][1] = resultArr[j][1] + 1;
       flag = false;
      }
  }
  if(flag){
    resultArr.push(Array(multipleDuplicateArr[i],1));
  }
}

console.log(resultArr);

You will get result in console as below:

[ 1, 4, 5, 2, 6, 8, 7, 5, 0, 5 ] . // multipleDuplicateArr
[ [ \'KEYS\', \'OCCURENCE\' ],        // resultArr
  [ 1, 1 ],
  [ 4, 1 ],
  [ 5, 3 ],
  [ 2, 1 ],
  [ 6, 1 ],
  [ 8, 1 ],
  [ 7, 1 ],
  [ 0, 1 ] ]

回答17:

This is my dummy answer that anyone can understand!

const duplicates = function(arr){
const dic = []
arr.forEach(function(val){
    if(!!dic[val]){
        dic[val]++
    }else{
        dic[val] = 1
    }
});
return dic
}