Grouping array data according to a id

Question

With a API call i'm receiving a response like below

[
  {
    stationId: "10"
    name: "Jinbaolai"
    group: {id: "18", stationGroupName: "Ali"}
  },
  {
    stationId: "13"
    name: "Stack"
    group: {id: "18", stationGroupName: "Ali"}
  },
  {
    stationId: "20"
    name: "Overflow"
    group: {id: "19", stationGroupName: "Baba"}
  }

]

As you can see first two records consist with the same group. I want to group these data according to the group. So for example it should look like this

[
  {
    groupId: "18",
    groupName : "Ali",
    stations : [
                 {
                  stationId: "10",
                  name: "Jinbaolai"
                 },
                 {
                  stationId: "13",
                  name: "Stack"
                 }
               ]

  },
  {
    groupId: "19",
    groupName : "Baba",
    stations : [
                 {
                  stationId: "20",
                  name: "Overflow"
                 },
               ]

  }

]

I want to do the grouping logic in my reducer where i also set the full data array that is shown in the beginning of the question.

            case EVC_SUCCESS:
            return {
                ...state,
                chargingStations: action.evcData.chargingStations,
                chargingStationGroups: //This is where my logic should go. ('action.evcData.chargingStations' is the initial data array)
                tableLoading: false
            }

How can i do this? I tried something using filter but not successful.

Answer 1

The best way to do this is to use Array.prototype.reduce()

Reduce is an aggregating function where you put in an array of something and get a single vaule back.

There may be a starting value as last parameter like I used {}. The signature is reduce(fn, startingValue) where fn is a function taking two parameters aggregate and currentValue where you return the aggregate in the end.

const groupData = (data)=> {

    return Object.values(data.reduce((group,n)=>{
    if (!group[n.group.id]){
        group[n.group.id] = {
      groupId:n.group.id,
      groupName: n.group.stationGroupName,
      stations:[]}
    } 
    group[n.group.id].stations.push({
      stationID: n.stationId,
      name: n.name
    })
    return group;
  }, {}))

}

Here is the fiddle

Answer 2

I think chaining multiple functions will work.

const stations = [
  {
    "stationId": 10,
    "name": "Jinbaolai",
    "group": {"id": "18", "stationGroupName": "Ali"}
  },
  {
    "stationId": 13,
    "name": "Stack",
    "group": {"id": 18, "stationGroupName": "Ali"}
  },
  {
    "stationId": 20,
    "name": "Overflow",
    "group": {"id": "19", "stationGroupName": "Baba"}
  }
]
const groups = _.chain(stations)
.groupBy((station) => { return station.group.id })
.map((values, key) => { 
  return {
    "groupId": _.first(values).group.id,
    "groupName": _.first(values).group.id,
    "stations": _.map(values,(value)=>{ return { "stationId": value.stationId, "name": value.name   } })
  }
})
console.log("groups",groups)

<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.15/lodash.min.js"></script>

Answer 3

A simple JS algorithm can do that for you

const list = [
  {
    stationId: "10",
    name: "Jinbaolai",
    group: {id: "18", stationGroupName: "Ali"}
  },
  {
    stationId: "13",
    name: "Stack",
    group: {id: "18", stationGroupName: "Ali"}
  },
  {
    stationId: "20",
    name: "Overflow",
    group: {id: "19", stationGroupName: "Baba"}
  }

];
const groups = {};

list.forEach((item) => {
  const groupId = item.group.id;
  const group = groups[groupId] || {groupId: groupId, groupName: item.group.stationGroupName, stations: []};

  group.stations.push({stationId: item.stationId, name: item.name});
  groups[groupId] = group;
});

const groupedArray = Object.keys(groups).map((groupId) => groups[groupId]);

console.log(groupedArray); // This will be the output you want