Nodejs: Object aggregation

Question

I am using Nodejs & would like to group my object array based on few attributes. example attr_id & type will be unique

const normalizedList =[ {
        "attr_id": 1,
        "type": "color",
        "value_index": 10,
        "value_label": "Blue"
    },
    {
        "attr_id": 1,
        "type": "color",
        "value_index": 15,
        "value_label": "Red"
    },
    {
        "attr_id": 2,
        "type": "size",
        "value_index": 10,
        "value_label": "Small"
    },
    {
        "attr_id": 2,
        "type": "size",
        "value_index": 14,
        "value_label": "Big"
    }
];

Needs to be converted to

[{
        "attr_id": 1,
        "type": "color",
        "values": [{
                "index": 10,
                "label": "Blue"
            }, {
                "index": 15,
                "label": "Red"
            }
        ]
    }, {
        "attr_id": 2,
        "type": "size",
        "values": [{
                "index": 10,
                "label": "Small"
            }, {
                "index": 14,
                "label": "Big"
            }
        ]
    }
]

I was trying to do this without any packages like "underscore" or "json-aggregate". as not many places in the code we do any grouping/aggregation

Below is how I was able to solve

const groupJson = (arr,g_label) =>{
// group the list by 'attr_id'
    const groupedAttrList = normalizedList.reduce((acc, obj)=>{
      let key = obj[g_label]
      if (!acc[key]) {
        acc[key] = []
      }
      acc[key].push(obj)
      return acc
    },{});
    const finalArray = [];

  // Now iterate over the groupedAttrList 
    for (let typeRow in groupedAttrList){
      let resultObj = {};
      let tempRow = groupedAttrList[typeRow];
      // as attr_id,type are unique for the set; picking it from 1st
      const {attr_id,type} = tempRow [0];
      resultObj .attr_id= attr_id;
      resultObj .type= type;
      // get all the values
      resultObj .values = tempRow .map(v=>{
        return {index:v.value_index,label:v.value_label};
      });
      finalArray.push(resultObj );
    }
    console.log(finalArray);
};

Test

let tempResult = groupJson(normalizedList,'attr_id');

wanted to learn if there are better ways to do it

JSON is a textual notation for data exchange. (More here.) If you're dealing with JavaScript source code, and not dealing with a string, you're not dealing with JSON. — T.J. Crowder
– T.J. Crowder, Commented Jan 22, 2022 at 11:16
compound data equality is a tough nut to crack in javascript. i think you will find this Q&A to be helpful. — Mulan
– Mulan, Commented Jan 22, 2022 at 14:26

The Bomb Squad · Accepted Answer · 2022-01-22 15:52:09Z

Well I guess you can make it more dynamic(something to group by an unknown amount of attributes)

First, I give you the answer in your output format in structure
[{values:[...objectsInGroup],...groupingInfo}, ...otherGroupObjects]

const myList=[{"attr_id":1,"type":"color","value_index":10,"value_label":"Blue"},{"attr_id":1,"type":"color","value_index":15,"value_label":"Red"},{"attr_id":2,"type":"size","value_index":10,"value_label":"Small"},{"attr_id":2,"type":"size","value_index":14,"value_label":"Big"}]
function groupList(list,attributes){
  var cache={} //for finding elements that have the same attributes
  for(let item of list){
    let ID=attributes.map(attr=>item[attr]).join('-')
    //items with same ID would be grouped together
    cache[ID]? cache[ID].values.push(item): cache[ID]={values:[item]}
    //if ID exists.. add to the group, else make the group
    attributes.forEach(key=>{
      if(!cache[ID][key]){ cache[ID][key]=item[key] }
    })
  }
  return Object.values(cache)
}

const newList=groupList(myList,['attr_id','type'])
console.log(newList)

But what if there was a values attribute that is in the original items in the list that you wanted it sorted by? only one value can exist per key.. in that case you can change the structure to
[{values:[...objectsInGroup],info:{...groupingInfo}} ...otherGroupObjects]

const myList=[{"attr_id":1,"type":"color","value_index":10,"value_label":"Blue"},{"attr_id":1,"type":"color","value_index":15,"value_label":"Red"},{"attr_id":2,"type":"size","value_index":10,"value_label":"Small"},{"attr_id":2,"type":"size","value_index":14,"value_label":"Big"}]
function groupList(list,attributes){
  var cache={} //for finding elements that have the same attributes
  for(let item of list){
    let ID=attributes.map(attr=>item[attr]).join('-')
    //items with same ID would be grouped together
    cache[ID]? cache[ID].values.push(item): cache[ID]={values:[item]}
    //if ID exists.. add to the group, else make the group
    if(!cache[ID].info){
      cache[ID].info={} //info about the grouping of this array
      attributes.forEach(key=>cache[ID].info[key]=item[key])
    }
  }
  return Object.values(cache)
}

const newList=groupList(myList,['attr_id','type'])
console.log(newList)

supertux · Accepted Answer · 2022-01-22 18:24:42Z

1

Im not necessarily sure if this is any better, but this is how I would maybe go about this. You could easily wrap this into a function

const finalObjects = [];
const checkIdInArray = (id) => finalObjects.find((obj) => obj.attr_id === id);

normalizedList.forEach((element) => {
  if (!checkIdInArray(element.attr_id)) {
    // Then add to array as its not been added yet
    finalObjects.push({
      attr_id: element.attr_id,
      type: element.type,
      values: [
        {
          index: element.value_index,
          label: element.value_label,
        },
      ],
    });
    return;
  }
  // Get the index of the existing id
  const arrIndex = finalObjects.findIndex((e) => e.attr_id === element.attr_id);
  finalObjects[arrIndex].values.push({
    index: element.value_index,
    label: element.value_label,
  });
});
console.log(JSON.stringify(finalObjects));

edited Jan 22, 2022 at 18:24

answered Jan 22, 2022 at 15:11

supertux

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1 Comment

karthikMI2 Over a year ago

Thanks for the answer, solution is simple & easy to understand

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