flatten a list of objects with nested lists of objects

Question

I have a javascript list in the form of:

var list = [{id:1, data: "string", list: [
              {id:2, data: "string", list: [
                {id:3, data: "string", list: null}]},
              {id:4, data: "string", list: null}]}];

And I want it to be in the form of:

var list = [{id:1, data: "string", list: \\ original nested list or null, I don't care},
            {id:2, data: "string", list:},
            {id:3, data: "string", list:},
            {id:4, data: "string", list:}];

I have access to underscore.js, but I haven't been able to produce the output I want. I tried using a combination of _.flatten and _.pluck to get the underlying list, but I also need the id property so this doesn't work. My guess is that I need to map a function, but I'm kind of lost on the issue right now.

Could anybody help me with this?

like this?

mjr
– mjr

2016-02-22 18:45:32 +00:00
Commented Feb 22, 2016 at 18:45 — mjr
– mjr, Commented Feb 22, 2016 at 18:45

madox2 · Accepted Answer · 2016-02-22 19:04:04Z

4

You can use recursion to do it:

function flatten(arr) {
    if (!arr) {
        return [];
    }
    return arr.reduce(function (r, i) {
        return r.concat([i]).concat(flatten(i.list));
    }, []);
}

console.log(flatten(list));

With ES6 syntax (arrow functions and spread operator) it could look like this:

function flatten(arr) {
    return arr ? arr.reduce((r, i) => [...r, i, ...flatten(i.list)], []) : [];
}

edited Feb 22, 2016 at 19:04

answered Feb 22, 2016 at 18:49

madox2

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1 Comment

Erik Deijl Over a year ago

Thanks, this is exactly what I wanted

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