Compare 2 array and form a new array based on values from both arrays?

Question

compare two array form an array based on name with percentage and days. I have done with map function but some much duplicates. Pls provide a better solution.

    const a = [{cname: 'a'},{cname: 'b'},{cname: 'c'},{cname: 'd'},{cname: 'e'},{cname: 'f'},{cname: 'g'},{cname: 'h'},{cname: 'i'},{cname: 'j'},{cname: 'k'},{cname: 'l'},{cname: 'm'}]
    
    const b = [{name: 'a', percentage: 10, days: 20, template: 'abc', id: '1'}, {name: 'e', percentage: 11, days: 21, template: 'cde', id: '2'}, {name: 'm', percentage: 12, days: 22, template: 'ghi', id: '3'}]
    
    result = [{name: 'a', percentage: 10, days: 20, template: 'abc', id: '1'},{name: 'b', percentage: 0, days: 0, template: '', id: ''},{name: 'c', percentage: 0, days: 0, template: '', id: ''},{name: 'd', percentage: 0, days: 0, template: '', id: ''}, {name: 'e', percentage: 11, days: 21, template: 'cde', id: '2'},{name: 'f', percentage: 0, days: 0, template: '', id: ''},{name: 'g', percentage: 0, days: 0, template: '', id: ''},{name: 'h', percentage: 0, days: 0, template: '', id: ''},{name: 'i', percentage: 0, days: 0, template: '', id: ''},{name: 'j', percentage: 0, days: 0, template: '', id: ''},{name: 'k', percentage: 0, days: 0, template: '', id: ''},{name: 'l', percentage: 0, days: 0, template: '', id: ''}, {name: 'm', percentage: 12, days: 22, template: 'ghi', id: '3'}],

    const result = [];
            a.filter(el => {
              b.filter(elm => {
                if (el.cname === elm.name) {
                  result.push(elm);
                } else {
                  result.push({
                   percentage: 0,
                   name: el.cname,
                    days: 0,
                    template: '',
                    id: ''
                  })
                }
              })
            })
console.log(result)

HI vishnu, Lemme get this clear, You have a solution but duplicate values are added to the array. am I right? — Joel Company
– Joel Company, Commented Mar 8, 2021 at 6:14

CertainPerformance · Accepted Answer · 2021-03-08 06:16:44Z

First group the a array into an object (or Map) indexed by ID, where the values of the object are the template (with percentage: 0 etc) combined with a name property. Then iterate through the other array, combining onto the associated object if there's a matching name:

    const a = [{cname: 'a'},{cname: 'b'},{cname: 'c'},{cname: 'd'},{cname: 'e'},{cname: 'f'},{cname: 'g'},{cname: 'h'},{cname: 'i'},{cname: 'j'},{cname: 'k'},{cname: 'l'},{cname: 'm'}]
    
const b = [{name: 'a', percentage: 10, days: 20, template: 'abc', id: '1'}, {name: 'e', percentage: 11, days: 21, template: 'cde', id: '2'}, {name: 'm', percentage: 12, days: 22, template: 'ghi', id: '3'}]

const template = { percentage: 0, days: 0, template: '', id: '' };
const grouped = Object.fromEntries(a.map(item => [item.cname, { name: item.cname, ...template }]));
for (const item of b) {
  if (grouped[item.name]) {
    Object.assign(grouped[item.name], item);
  }
}
console.log(Object.values(grouped));

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