Flatten an array of array and combine with another array in typescript

Question

According to this article you can flatten an array using concat.

For example;

const nestedArrays: Person[][] = [
    [
        {firstName: "Andrew", lastName: "Smith"},

    ],
    [
        {firstName: "Chris", lastName: "Cawlins"},
    ],
    [
        {firstName: "Susan", lastName: "Sarandon"},
    ]
]

will can be converted to

const flattenedArray: Person[] = [
    {firstName: "Andrew", lastName: "Smith"},
    {firstName: "Chris", lastName: "Cawlins"},
    {firstName: "Susan", lastName: "Sarandon"},
]

by using

const flattenedArray = [].concat(...nestedArrays);

I have an additional array like the follows,

const additional = ["extra1", "extra2"];

My end result should be

[
 ["extra1", "extra2"],
 [{firstName: "Andrew", lastName: "Smith"}],
 [{firstName: "Chris", lastName: "Cawlins"}],
 [{firstName: "Susan", lastName: "Sarandon"}],
]

Can I achieve that using concat in typescript? Or is there another method that I would be using?

Possible duplicate of merge two object arrays with Angular 2 and TypeScript? — leonardkraemer
– leonardkraemer, Commented Jan 2, 2019 at 18:24
The difference is if I use additional.concat(nestedArray), it would end up in something like ["extra1", "extra2", <rest of the things>] which I do not want in this case — SanD
– SanD, Commented Jan 2, 2019 at 18:31
How about if you define const additional = [["extra1", "extra2"]]; — leonardkraemer
– leonardkraemer, Commented Jan 2, 2019 at 18:33
The result is still array of arrays, so I don't see a reason for flattening. const flattenedArray = [additional].concat(nestedArrays); — Slai
– Slai, Commented Jan 2, 2019 at 18:34
Both the above suggestions work const additional = [["extra1", "extra2"]]; and const flattenedArray = [additional].concat(nestedArrays); — SanD
– SanD, Commented Jan 2, 2019 at 19:08

leonardkraemer · Accepted Answer · 2019-01-02 18:38:26Z

0

You dont have to flatten anything just use unshift to prepend:

const nestedArrays: Person[][] = [
    [
        {firstName: "Andrew", lastName: "Smith"},

    ],
    [
        {firstName: "Chris", lastName: "Cawlins"},
    ],
    [
        {firstName: "Susan", lastName: "Sarandon"},
    ]
]
const additional = ["extra1", "extra2"];
const combination = nestedArrays.unshift(additional);

answered Jan 2, 2019 at 18:38

leonardkraemer

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1 Comment

Slai Over a year ago

I was thinking the same, but that would probably result in TypeScript compilation error because the additional array is not Person type. It will probably have to be changed to any[][] type

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