JavaScript How to find and count duplicate integers in an array with javascript find duplicate count in excel,find duplicate count in sql,

If I understand correctly, you could achieve this via Array#reduce() as shown below:

let duplicateArr = [5, 3, 7, 4, 7, 5, 3, 2, 7, 3, 2];

/* Reduce the input duplicateArr to a map relating values to counts */
const valueCounts = duplicateArr.reduce((counts, value) => {
  
  /* Determine the count of current value from the counts dictionary */
  const valueCount = (counts[ value ] === undefined ? 0 : counts[ value ])
  
  /* Increment count for this value in the counts dictionary */
  return { ...counts, ...{ [value] : valueCount + 1 } }
  
}, {})

/* Remove values with count of 1 (or less) */
for(const value in valueCounts) {
  if(valueCounts[value] < 2) {
    delete valueCounts[value]
  }
}

/* Display the values and counts */
for(const value in valueCounts) {
  console.log(`${ value } occours ${ valueCounts[value] } time(s)` )
}

Answer:1

Reasonably basic loop approach

const data = [1, 1, 1, 1, 1, 100, 3, 5, 2, 5, 2, 23, 23, 23, 23, 23, ]

function dupCounts(arr) {
  var counts = {};
  arr.forEach(function(n) {
   // if property counts[n] doesn't exist, create it
    counts[n] = counts[n] || 0;
    // now increment it
    counts[n]++;
  });
  
  // iterate counts object and remove any that aren't dups
  for (var key in counts) {
    if (counts[key] < 2) {
      delete counts[key];
    }
  }

  return counts
}

console.log(dupCounts(data))

Answer:2

Here using only 1 loop.

let duplicateArr = [5, 3, 7, 4, 7, 5, 3, 2, 7, 3, 2]
let sortArr = duplicateArr.sort()
let current = 0, counter = 0
sortArr.forEach(n => {
  if (current === n) {
    counter++
  }
  else  {
    if (counter > 1){
      console.log(current + " occurs " + counter + " times.")
    }
    counter = 1
    current = n
  }
})
if (counter > 1){
  console.log(current + " occurs " + counter + " times.")
}

Answer:3

The cleanest way is using ES6 Map

function duplicates(arr) {
    // This will be the resulting map
    const resultMap = new Map();
    // This will store the unique array values (to detect duplicates using indexOf)
    const occurrences = [];

    for (let i of arr){
        if (occurrences.indexOf(i) !== -1) {
            // Element has a duplicate in the array, add it to resultMap
            if (resultMap.has(i)) {
                // Element is already in the resultMap, increase the occurrence by 1
                resultMap.set(i, resultMap.get(i) + 1);
            } else {
                // Element is not in resultMap, set its key to 2 (the first 2 occurrences)
                resultMap.set(i, 2);
            }
        } else {
            // Element is showing for the first time (not a duplicate yet)
            occurrences.push(i);
        }
    }
    return resultMap;
}

// To iterate on the map keys and values use this
for (const [key, value] of map) {
    console.log(key + ' - ' + value + ' times');
}

Answer:4

You can just iterate over all of the unique values and then count how many of them exists.

here is a sample code:

let duplicateArr = [5, 3, 7, 4, 7, 5, 3, 2, 7, 3, 2];
let sortArr = duplicateArr.sort();
let newArr = {};
let duplicateValues = [];
for (let i = 0; i < duplicateArr.length; i++) {
  let count = 0;
  let k = 0;
  while (i + k < duplicateArr.length && sortArr[i] == sortArr[i + k]) {
    count++;
    k++;
  }
  if (count > 1) {
    newArr[sortArr[i]] = count;
    duplicateValues.push(sortArr[i]);
  }
  i = i + k;
}

console.log("duplicate items with count:", newArr);
console.log("duplicate items:", duplicateValues);

Answer:5

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