functional programming way to flat arrays in javascript object

Question

I am very new in javascript and I am trying to flatten attribute in an object which save in an array of objects.

[
 {
  addr: addrvalue1,
  events: [1,2],
 },
 {
  addr: addrvalue2,
  events: [1],
 }
]

I want to convert objects above to

[{
 addr: addrvalue1,
 events: 1,
}
{
 addr: addrvalue1,
 events: 2,
}
{
 addr: addrvalue2,
 events: 1,
}]

And then sort them by event value, so they will finally be like

[{
     addr: addrvalue1,
     events: 1,
    }
{
     addr: addrvalue2,
     events: 1,
    }
    {
     addr: addrvalue1,
     events: 2,
    }
]

For now I am using multiple for-loops for to do this, but I think there would be some more elegant way doing this. Thanks in advance.

Ori Drori · Accepted Answer · 2018-11-24 13:27:35Z

2

You can use Array.flatMap() to iterate the objects and flatten the results, and an internal Array.map() to create the arrays of event objects. Then you can sort them by the event.

const data = [{"addr":"addrvalue1","events":[1,2]},{"addr":"addrvalue2","events":[1]}]

const result = data.flatMap(({ addr, events }) => events.map(event => ({
    event,
    addr
  })))
  .sort((o1, o2) => o1.event - o2.event)
  
console.log(result)

edited Nov 24, 2018 at 13:27

answered Nov 24, 2018 at 13:17

Ori Drori

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2 Comments

kemicofa Over a year ago

Good use of flatMap

Ori Drori Over a year ago

Because flatMap is not supported by IE and Edge. If you need a support for those browsers use @kemicofa's answer.

kemicofa · Accepted Answer · 2018-11-24 13:17:43Z

1

Use Array#reduce with Array#concat

const data = [{
    addr: 111,
    events: [1, 2],
  },
  {
    addr: 222,
    events: [1],
  }
];

const result = data.reduce((acc, {addr, events})=>{
  return acc.concat(events.map(item=>({addr, events: item})));
}, []);

console.log(result.sort((a,b)=>a.events-b.events));

answered Nov 24, 2018 at 13:17

kemicofa

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Comments

FZs · Accepted Answer · 2018-11-24 13:23:55Z

0

Something like this?

var output=[],
    data=[
 {
  addr: "addrvalue1",
  events: [1,2],
 },
 {
  addr: "addrvalue2",
  events: [1],
 }
]
for(obj of data){
  for(i in obj.events){
    output.push({addr:obj.addr,events:parseInt(i)+1})
  }
}
output.sort(function(a,b){return a.events-b.events})
console.log(output)

I hope it will helps :)

answered Nov 24, 2018 at 13:23

FZs

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