Search values of multiple keys with same name of items in array

Question

I've an array like this:

const myArray = ['Item1', 'Item3', 'Item5'];

And an object list like that:

ObjectsList: {
    Item1: ["A", "B", "C"],
    Item2: ["A", "D", "E"],
    Item3: ["B", "E", "C", "G"],
    Item4: ["B", "C", "R"],
    Item5: ["D"],
    Item6: ["F", "D", "E"],
    Item7: ["A", "E", "L", "M"],
}

I want to get the values of all the keys with the same name of my array elements and push them into a new array without duplicate elements.

In the case of my provided example I want to get the Item1, Item3, Item5 keys values and push them in a new array avoiding duplicates. The result should be that: [A, B, C, E, G, D]

Which is the best way to do that in JavaScript? Thanks in advance.

Nick Parsons · Accepted Answer · 2020-08-14 16:08:39Z

You can .flatMap() your myArray to an array of characters from the ObjectsList, and then use a Set to remove the duplicate characters. Lastly, you can use the spread syntax (...) to convert the set into an array:

const objectsList = { Item1: ["A", "B", "C"], Item2: ["A", "D", "E"], Item3: ["B", "E", "C", "G"], Item4: ["B", "C", "R"], Item5: ["D"], Item6: ["F", "D", "E"], Item7: ["A", "E", "L", "M"], };
const myArray = ['Item1', 'Item3', 'Item5'];

const res = [...new Set(myArray.flatMap(k => objectsList[k]))];
console.log(res);

If you can't support .flatMap(), you can use a regular .map(), and then use .concat() to perform the flattening:

const objectsList = { Item1: ["A", "B", "C"], Item2: ["A", "D", "E"], Item3: ["B", "E", "C", "G"], Item4: ["B", "C", "R"], Item5: ["D"], Item6: ["F", "D", "E"], Item7: ["A", "E", "L", "M"], };
const myArray = ['Item1', 'Item3', 'Item5'];

const res = [...new Set([].concat(...myArray.map(k => objectsList[k])))];
console.log(res);

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