Splitting the values of an array based on a property and then form a new array of objects

Question

I have an objects that contains arrays with following structure:

var obj  = {
  "feature1" : ["val1","val2"],
  "feature2" : ["val3"]
}

Now I want to split the values that are present inside of this each array and form a new array of objects that should like :

var result = [
  {
    "field": "feature1",
    "value": "val1",
    "type": "add"
  },
  {
    "field": "feature1",
    "value": "val2",
    "type": "add"
  },
  {
    "field": "feature2",
    "value": "val3",
    "type": "add"
  }
]

Here splitting must happen based on the "field" and it show something that is similar to above.here "type" is an extra field that is hardcoded

Help would be appreciated.

Loop through the keys of the object and inside that, loop through each value array. Please add the code you've tried so far — adiga, Jul 24 '19 at 07:36

Kobe · Accepted Answer · 2019-07-24T12:23:55.023

You can get key/value pairs, loop over them, then loop over each value in each array, and push each value into an object, back into the accumulator

var obj = {
  "feature1": ["val1", "val2"],
  "feature2": ["val3"]
}

const output = Object.entries(obj)
  .reduce((a, [k, v]) => a
    .concat(v
      .map(e => ({
        field: k,
        value: e,
        type: 'add'
      })
    )
  ), [])


console.log(output)

Or, as a one-line less readable version:

var obj = {
  "feature1": ["val1", "val2"],
  "feature2": ["val3"]
}

const output = Object.entries(obj).reduce((a, [k, v]) => a.concat(v.map(e => ({field: k, value: e, type: 'add'}))), [])

console.log(output)

For a more performance-oriented solution, you should use plain old for loops:

var obj = {
  "feature1": ["val1", "val2"],
  "feature2": ["val3"]
}

const out = []

for (var o in obj) {
  const arr = obj[o]
  for(var i = 0; i < arr.length; i++) {
    out.push({
      field: o,
      value: arr[i],
      type: 'add'
    })
  }
}

console.log(out)

Here is a JSPerf to show the performance difference

Edit:

var obj = {
  "feature1": ["1", "1", "2", "3", "1"],
  "feature2": ["val3"]
}

const output = Object.entries(obj).reduce((a, [k, v]) => a.concat([...new Set(v)].map(e => ({field: k, value: e, type: 'add'}))), [])

console.log(output)

Thank you . It worked. How can I avoid duplicate values , if there is one under that field? Say there is something "feature1" : ["1","2","1"], Do not want multiple values of 1 — joy08, Jul 24 '19 at 11:57
@vrosario You could use a set to remove them, I'll add an edit now. — Kobe, Jul 24 '19 at 12:21

Splitting the values of an array based on a property and then form a new array of objects

1 Answers1