Filter and Combine Nested Array in ES6

Question

I need to combine the gid and subGroups and output it into an array of strings without duplication. My problem now is that it only gets the first level.

const oldGroup = [
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "SFO",
        "subGroups": []
    },
    {
        "gid": "LAX",
        "subGroups": [
            "LGA"
        ]
    }
]

const newGroup = [...new Set(oldGroup.map((group) => group.gid))]

console.log(newGroup)

What’s the expected result? Are you looking for const newGroup = Array.from(new Set(oldGroup.flatMap(({ gid, subGroups }) => subGroups.map((item) => `${gid} → ${item}`))))? — Sebastian Simon
– Sebastian Simon, Commented Dec 2, 2022 at 4:07

Peter Thoeny · Accepted Answer · 2022-12-02 23:06:11Z

2

There are several ways to achieve this, here is one with .reduce():

const oldGroup = [
    { "gid": "JFK", "subGroups": [ "SFO", "LAX" ] },
    { "gid": "JFK", "subGroups": [ "SFO", "LAX" ] },
    { "gid": "SFO", "subGroups": [] },
    { "gid": "LAX", "subGroups": [ "LGA" ] }
];

const newGroup = Object.keys(oldGroup.reduce((acc, obj) => {
  acc[obj.gid] = true;
  obj.subGroups.forEach(name => { acc[name] = true; } );
  return acc;
}, {}));

console.log(newGroup)

Explanation:

The .reduce() has two parameters:
- a function parameter with two options acc, obj. The former is the accumulator that keeps track of the data needed, the latter is the array item object
- an initial setting, and empty {} object in our case
Object.keys() is applied on the accumulated data

edited Dec 2, 2022 at 23:06

answered Dec 2, 2022 at 4:19

Peter Thoeny

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Comments

CertainPerformance · Accepted Answer · 2022-12-02 04:08:51Z

1

With .flatMap instead of .map, return an array in the callback - the .gid value, and also spread in the .subGroups array.

const oldGroup = [
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "SFO",
        "subGroups": []
    },
    {
        "gid": "LAX",
        "subGroups": [
            "LGA"
        ]
    }
]

const newGroup = [...new Set(oldGroup.flatMap((group) => [group.gid, ...group.subGroups]))]

console.log(newGroup)

answered Dec 2, 2022 at 4:08

CertainPerformance

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3 Comments

Hunter McMillen Over a year ago

Array.from(new Set(...)) maybe?

CertainPerformance Over a year ago

That's equivalent to [...new Set()] here

Hunter McMillen Over a year ago

It seems harder to read, that might just be me.

Dhammika · Accepted Answer · 2022-12-02 04:22:35Z

You can use the Array.prototype.map() and Array.prototype.flat() methods to transform the oldGroup array into a new array that only contains the gid and subGroups values. You can then use the Array.prototype.filter() method to remove any duplicate values from the new array.

const oldGroup = [
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "JFK",
        "subGroups": [
            "SFO",
            "LAX"
        ]
    },
    {
        "gid": "SFO",
        "subGroups": []
    },
    {
        "gid": "LAX",
        "subGroups": [
            "LGA"
        ]
    }
]
// Transform the oldGroup array into a new array that only contains the gid and subGroups values
const newGroup = oldGroup.map(group => [group.gid, ...group.subGroups]).flat();

// Remove any duplicate values from the new array
const dedupedGroup = newGroup.filter((value, index) => newGroup.indexOf(value) === index);

console.log(dedupedGroup); // ["JFK", "SFO", "LAX", "SFO", "LAX", "SFO", "LAX", "LGA"]

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