Concat array from Object from Array

Question

I'm currently trying to retrieve a list of metadata stored as an array, inside an object, inside an array. Here's a better explanatory example:

[
    {
        name: 'test',
        metadata: [
            {
                name: 'Author',
                value: 'foo'
            },
            {
                name: 'Creator',
                value: 'foo'
            }
        ]
    },
    {
        name: 'otherTest',
        metadata: [
            {
                name: 'Created',
                value: 'foo'
            },
            {
                name: 'Date',
                value: 'foo'
            }
        ]
    },
    {
        name: 'finalTest'
    }
]

Now, my objective is to retrieve a list of metadata (by their name) without redundancy. I think that .map() is the key to success but I can't find how to do it in a short way, actually my code is composed 2 for and 3 if, and I feel dirty to do that.

The expected input is: ['Author', 'Creator', 'Created', 'Date']

I'm developping in Typescript, if that can help for some function.

what do you need from metadata? the whole object or just parts? — Nina Scholz
– Nina Scholz, Commented Dec 8, 2016 at 13:37

Nenad Vracar · Accepted Answer · 2016-12-08 14:07:59Z

3

You can use reduce() and then map() to return array of names.

var data = [{"name":"test","metadata":[{"name":"Author","value":"foo"},{"name":"Creator","value":"foo"}]},{"name":"otherTest","metadata":[{"name":"Created","value":"foo"},{"name":"Date","value":"foo"}]},{"name":"finalTest"}]

var result = [...new Set(data.reduce(function(r, o) {
  if (o.metadata) r = r.concat(o.metadata.map(e => e.name))
  return r
}, []))];


console.log(result)

edited Dec 8, 2016 at 14:07

answered Dec 8, 2016 at 13:42

Nenad Vracar

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2 Comments

Nina Scholz Over a year ago

it looks, you concat any name, you get in the array, without checking for uniqueness.

Nenad Vracar Over a year ago

@Nina Scholz Yea my bad, fixed it.

Nina Scholz · Accepted Answer · 2016-12-08 13:43:44Z

2

You could use Set for unique names.

var data = [{ name: 'test', metadata: [{ name: 'Author', value: 'foo' }, { name: 'Creator', value: 'foo' }] }, { name: 'otherTest', metadata: [{ name: 'Created', value: 'foo' }, { name: 'Date', value: 'foo' }] }, { name: 'finalTest' }],
    names = new Set;

data.forEach(a => (a.metadata || []).forEach(m => names.add(m.name)));

console.log([...names]);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Dec 8, 2016 at 13:43

Nina Scholz

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Comments

Filipe Roberto · Accepted Answer · 2016-12-08 13:51:07Z

1

var data = [{"name":"test","metadata":[{"name":"Author","value":"foo"},{"name":"Creator","value":"foo"}]},{"name":"otherTest","metadata":[{"name":"Created","value":"foo"},{"name":"Date","value":"foo"}]},{"name":"finalTest"}]

data
.filter(function(obj){return obj.metadata != undefined})
.map(function(obj){return obj.metadata})
.reduce(function(a,b){return a.concat(b)},[])
.map(function(obj){return obj.name})

answered Dec 8, 2016 at 13:51

Filipe Roberto

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Comments

Redu · Accepted Answer · 2016-12-08 17:28:55Z

1

A hand to hand Array.prototype.reduce() and Array.prototype.map() should do it as follows;

var arr = [
    {
        name: 'test',
        metadata: [
            {
                name: 'Author',
                value: 'foo'
            },
            {
                name: 'Creator',
                value: 'foo'
            }
        ]
    },
    {
        name: 'otherTest',
        metadata: [
            {
                name: 'Created',
                value: 'foo'
            },
            {
                name: 'Date',
                value: 'foo'
            }
        ]
    },
    {
        name: 'finalTest'
    }
];

result = arr.reduce((p,c) => c.metadata ? p.concat(c.metadata.map(e => e.name))
                                        : p, []);
console.log(result);

answered Dec 8, 2016 at 17:28

Redu

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2 Comments

LoïcR Over a year ago

It seems to not work anymore in my typescript code, is it related to a new update or something?

Redu Over a year ago

There are some type coercions going on tin this snippet such as c.metadata ? ... I am not sure if you can do these in TypeScript. From the name i suspect it must be strict on types. Did it ever work with TypeScript and now stopped working?

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