Manipulate an array of objects inside another array

Question

I'm having a problem manipulating an array of objects inside another array.I created an example to explain what I need. So here we have this array:

array1 =
[
    {
        "first": "A",
        "second": [
            "one"
        ]
    },
    {
        "first": "A",
        "second": [
            "three"
        ]
    },
    {
        "first": "C",
        "second": [
            "four"
        ]
    },
    {
        "first": "D",
        "second": [
            "one"
        ]
    },
    {
        "first": "C",
        "second": [
            "three"
        ]
    },
]

I've been trying to create a logic to manipulate this array and return something like this:

result = 
[
    {
        "first": "A",
        "second": [
            "one",
            "three"
        ]
    },
    {
        "first": "C",
        "second": [
            "three",
            "four"
        ]
    },
    {
        "first": "D",
        "second": [
            "one"
        ]
    },
]

You can improve your chances of getting help by presenting what you've tried and what's going wrong with it. Also, see here for an inspiration about what to try... https://stackoverflow.com/questions/14446511/most-efficient-method-to-groupby-on-an-array-of-objects — danh, May 16 '22 at 16:24

score 0 · Answer 1 · 2022-05-16T16:48:22.287

0

for(let i = 0, n = result.length; i < n; ++i) {

   for(let k = 0, l = result[i].second.length; k < l; ++k) {
  
     result[i].second.push("anything");
  
   }

 }

edited May 16 '22 at 16:48

answered May 16 '22 at 16:28

score 0 · Answer 2 · answered May 16 '22 at 16:30

0

Could you try this ?

let result = [];

array1.forEach(obj => {
  if(!result[obj.first]) {
    result[obj.first] = {
      first: obj.first
      , second: []
    }
  }

  result[obj.first].second.push(obj.second[0])
})

answered May 16 '22 at 16:30

Guillaume

319
1
11

score 0 · Accepted Answer · answered May 16 '22 at 16:46

You can go with the following approach:

array1 =
[
    {
        "first": "A",
        "second": [
            "one"
        ]
    },
    {
        "first": "A",
        "second": [
            "three"
        ]
    },
    {
        "first": "C",
        "second": [
            "four"
        ]
    },
    {
        "first": "D",
        "second": [
            "one"
        ]
    },
    {
        "first": "C",
        "second": [
            "three"
        ]
    },
]

var array2 = []

array1.forEach(function(item) {
  var existing = array2.filter(function(v, i) {
    return v.first == item.first;
  });
  if (existing.length) {
    var existingIndex = array2.indexOf(existing[0]);
    array2[existingIndex].second = array2[existingIndex].second.concat(item.second);
  } else {
    if (typeof item.second == 'string')
      item.second = [item.second];
    array2.push(item);
  }
});

console.log(array2);

Manipulate an array of objects inside another array

3 Answers3