JS Filter Array To Remove Duplicate Values Based On Condition

I have an array containing duplicate elemnets let myArray=[ {role: 'role-1', deviceId: ''}, {role: 'role-2', deviceId: 'd-2'}, {role: 'role-3', deviceId: 'd-3'},

Solution 1:

You can use reduce with default to object, and if you need, you can convert it to array at the end.

let myArray = [
     {role: "role-1", deviceId: ""},
     {role: "role-2", deviceId: "d-2"},
     {role: "role-3", deviceId: "d-3"},
     {role: "role-1", deviceId: "d-1"},
     {role: "role-2", deviceId: ""},
     {role: "role-4", deviceId: ""},
     {role: "role-5", deviceId: ""}
]

const res = myArray.reduce((agg, itr) => {
  if (agg[itr.role]) return agg // if deviceId already exist, skip this iteration
  agg[itr.role] = itr.deviceId  // if deviceId not exist, Add it
  return agg
}, {})

let make_array = Object.keys(res).map(key => { return { role: key, deviceId: res[key] }})

console.log(make_array)

Solution 2:

You can map the unique role to an object and reduce the object to an array as following code snippet

let myArray = [
     {role: "role-1", deviceId: ""},
     {role: "role-2", deviceId: "d-2"},
     {role: "role-3", deviceId: "d-3"},
     {role: "role-1", deviceId: "d-1"},
     {role: "role-2", deviceId: ""},
     {role: "role-4", deviceId: ""},
     {role: "role-5", deviceId: ""}
];

var uniqueObj = myArray.reduce(function(acc, item) {
  var deviceId = acc[item.role] && acc[item.role].deviceId || item.deviceId;
  acc[item.role] = item;
  acc[item.role].deviceId = deviceId;
  return acc;
}, {});

var result = Object.keys(uniqueObj).reduce(function(acc2, item) {
  acc2.push(uniqueObj[item]);
  return acc2;
}, []);

console.log(result);

Solution 3:

You could apply a filter an look ahead in the array for duplicates to decide to filter the index or keep it

const myArray= [
     {role: "role-1", deviceId: ""},
     {role: "role-2", deviceId: ""},
     {role: "role-3", deviceId: "d-3"},
     {role: "role-1", deviceId: "d-1"},
     {role: "role-2", deviceId: ""},
     {role: "role-4", deviceId: ""},
     {role: "role-5", deviceId: ""}
]
  
const cleanArray = myArray.filter( (item,index,array) => {
  if ( item.deviceId === "") {
    // filter it out when the same role is found in the array and the index isn't the same as current item you are looking at 
    return !array.some((i,idx) => i.role === item.role && idx > index  )
  }
  return true 
})

// for presentation: sort the array
const sortedArray = cleanArray.sort( (curr, next) => curr.role >  next.role? 1:-1);

console.log(sortedArray)

Solution 4:

I'd group by role, then take the first with an deviceId:

  function groupBy(array, key) {
    const result = { };
    for(const el of array) {
      if(!result[ el[key] ]) result[ el[key] ] = [];
       result[ el[key] ].push(el);
   }
  return result;
}

const result = [];
const grouped = groupBy(myArray, "role");
for(const group of Object.values(grouped)) {
  result.push(group.find(it => it.deviceId) || group[0]);
}