How can I reduce elements in object?

debugcn Published at Dev

Jack23

I have an object like this:

result: 
     > rows:
       > 0: {key: Array(4), value: 3}
          > key: (4) ["Person", "2020-06-24", "Product, "00000000008"]
            value: 3
       > 1: {key: Array(4), value: 10}
          > key: (4) ["Person", "2020-06-25", "Product, "00000000009"]
            value: 10
       > 2: {key: Array(4), value: 10}
          > key: (4) ["Person", "2020-06-25", "Product, "00000000008"]
            value: 10

Now, what I need to do is to reduce this result checking for the same code (for example 00000000008) and sum the value, to obtain:

(for example)

00000000008   value: 13

Now, my problem is how to do, I have tried to use first a map and then a reduce, but I don't understand how can I check for the same code and sum the value.

How can I do?

I have tried in this way, but it doesn't work:

res is the object with the values

let example = res.rows.map((element)=> {
        console.log("ELEMENT IS ", element)
        let example1 = element.key[3].reduce(function(element, v){
          if(ref.hasOwnProperty(v))
            element[ref[v]] += v;
          else {
            ref[v] = element.length;
            element.push(prev = v)
          }
          return element
        }, [])
      })
      console.log("element", element)

DDomen

The Array.map method is useful for data transformations, but if you have to aggregate is mostly expensive because you have also to Array.filter the non-aggregated values.

You can use Array.reduce (MDN) instead in order to build your own object:

let result = {
  rows: [
    {
      key: ["Person", "2020-06-24", "Product", "00000000008"],
      value: 3
    },
    {
      key: ["Person", "2020-06-25", "Product", "00000000009"],
      value: 10
    },
    {
      key: ["Person", "2020-06-25", "Product", "00000000008"],
      value: 10
    }
  ]
}

let output1 = result.rows.reduce((acc, current) => {
  let key = current.key[3];
  // adding value to the accumulator
  acc[key] = (acc[key] || 0) + current.value;
  return acc;
}, {});

console.log(output1);

let output2 = result.rows.reduce((acc, current) => {
  // check if key is already present
  let found = acc.find(v => v.key == current.key[3])
  // if it is, update the current value
  if (found) {
    found.value += current.value;
  }
  // otherwise create a new one
  else {
    acc.push({ key: current.key[3], value: current.value });
  }
  return acc;
}, []);

console.log(output2)

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