How to sort JSON into an array based on a child property

Question

I've got an RESTful call that's returning data that resembles the following:

[{
  name: "one",
  dayID: "Tuesday},
 {
   name: "two",
   dayID: "Monday"
 },
 {
   name: 'three'
   dayID: "Tuesday
 }]

What I'm trying to do is iterate over the data and create a new array that has a nested structure based on a unique attribute. So if the array already has a Monday, push the json to that object. If not, make a new one. In this case nesting all objects under the day, so the new array would look like this:

[{"Monday":["two"]}, {"Tuesday":["one", "three"]}]

These won't be strings in practice, they'll be additional objects but for the sake of simplicity I'm asking for strings in my example. Any help is appreciated.

Show what you have tried. There are lots and lots of similar questions on this site. The objective here isn't to write code for you but to help you fix your code — charlietfl
– charlietfl, Commented Aug 7, 2017 at 17:44
I haven't tried anything yet, I wanted to see how people would approach this. — Aaron Case
– Aaron Case, Commented Aug 7, 2017 at 17:45

Nenad Vracar · Accepted Answer · 2017-08-07 17:46:29Z

4

Instead of array you could just return object since keys will be unique.

var data = [{
  name: "one",
  dayID: "Tuesday"
}, {
  name: "two",
  dayID: "Monday"
}, {
  name: 'three',
  dayID: "Tuesday"
}]

var result = data.reduce(function(r, e) {
  if (!r[e.dayID]) r[e.dayID] = [e.name];
  else r[e.dayID].push(e.name);
  return r;
}, {})

console.log(result)

answered Aug 7, 2017 at 17:46

Nenad Vracar

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Comments

Ori Drori · Accepted Answer · 2017-08-07 17:49:25Z

1

Use Array#reduce with a helper object:

var arr = [{
    name: "one",
    dayID: "Tuesday"
  },
  {
    name: "two",
    dayID: "Monday"
  },
  {
    name: 'three',
    dayID: "Tuesday"
  }
];


var helperObj = {};
var result = arr.reduce(function(r, o) {
  if(!helperObj[o.dayID]) {
    helperObj[o.dayID] = [];
    r.push({ [o.dayID]: helperObj[o.dayID] });
  }
  
  helperObj[o.dayID].push(o.name);

  return r;
}, []);

console.log(result);

answered Aug 7, 2017 at 17:49

Ori Drori

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Comments

Anurag Singh Bisht · Accepted Answer · 2017-08-07 18:06:53Z

1

You can make use of Array.reduce to update your array into the desired format.

You just need to keep updating the accumulating array acc as per the condition.

var data = [{
  name: "one",
  dayID: "Tuesday"},
 {
   name: "two",
   dayID: "Monday"
 },
 {
   name: 'three',
   dayID: "Tuesday"
 }];
 
 data = data.reduce((acc, cur) => {
  if(acc.some(a => a[cur.dayID])) {
    acc.forEach(a => {
       if(a[cur.dayID]) {
         a[cur.dayID].push(cur.name)
       }
    });
  } else {
    var obj = {};
    obj[cur.dayID] = [cur.name];
    acc.push(obj);
  }
  return acc;
 }, []);
 
 console.log(data);

edited Aug 7, 2017 at 18:06

answered Aug 7, 2017 at 17:49

Anurag Singh Bisht

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