Manipulate an array of objects inside another array

May 16, 2022

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"
        ]
    },
]

>Solution :

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);