How To Get Repeated Objects In Json Array In Javascript

I have a JSON array like this : var data = [ {title: 'HH02'}, {title: 'HH03'}, {title: 'HH04'}, {title: 'HH02'}, {title: 'HH07'}, {title: 'HH08'

Solution 1:

You can use reduce, filter and map

• Group all the values by title first, count there repetition
• Filter the titles which appears once or less then once ( exclude them )
• map them to get desired output

var data = [{title: "HH02"},{title: "HH03"},{title: "HH04"},{title: "HH02"},{title: "HH07"},{title: "HH08"},{title: "HH08"},{title: "HH10"},{title: "HH02"},{title: "HH11"}]

let final = [...data.reduce((op, inp) => {
  let title = inp.title
  op.set(title, (op.get(title) || 0) + 1)
  return op
}, new Map()).entries()].filter(([_,repeat]) => repeat > 1).map(([title, repeat]) => ({
  title,
  repeat
}))

console.log(final)

Solution 2:

You can use lodash groupBy for that.

Here is the link https://lodash.com/docs/4.17.15#groupBy

It will return a JSON object with titles as key and the array of items under that key as its value.

The length of that value will return the required count.

Solution 3:

I would never suggest having side effects in a sort callback other than sorting the array itself. Try a reduce followed by a filter and map on Object.keys(...):

const countMap = data.reduce((result, element) => {
    result[element.title] = (result[element.title] || 0) + 1;
    return result;
}, {});
const result = Object.keys(countMap).filter(title => countMap[title] > 1).map(title => {
    return {title, repeat: countMap[title]};
});

Solution 4:

You can count repeated objects with reduce and filter them out with filter

Object.values(data.reduce((acc, value) => {
  const repeat = acc[value.title] ? acc[value.title].repeat + 1 : 1;
  acc[value.title] = { repeat: repeat, ...value };
  return acc;
}, {})).filter(value => value.repeat > 1);