How to combine filter and reduce on arrays in javascript

Question

I have 2 arrays

var a = [{id: 1, name:"SFO"}, {id:2, name:"ATL"}];

var b = [{number: 1, sourceId:1, destinationId:2}, {number:2, sourceId:2, destinationId:1}];

I want to return an array in this form:

[{source: {name: "SFO"}, destination: {name: "ATL"}}, {source: {name:"ATL"}, destination: {name: "SFO"}}]

How can i use filter and reduce to produce this result above

Why reduce? map and filter should suffice

haim770
– haim770

2016-12-13 11:24:31 +00:00
Commented Dec 13, 2016 at 11:24 — haim770
– haim770, Commented Dec 13, 2016 at 11:24
@haim770 how can i use map and filter

EI-01
– EI-01

2016-12-13 11:30:47 +00:00
Commented Dec 13, 2016 at 11:30 — EI-01
– EI-01, Commented Dec 13, 2016 at 11:30

CroMagnon · Accepted Answer · 2016-12-13 12:05:54Z

1

The code which gets expected array:

var a = [{id: 1, name:"SFO"}, {id:2, name:"ATL"}];
var b = [{number: 1, sourceId:1, destinationId:2}, {number:2, sourceId:2,  destinationId:1}];

var arr = [];
for(var i=0; i<b.length; i++){
    arr.push({
        source: {name: findName(b[i].sourceId, a) },
        destination: {name: findName(b[i].destinationId, a) }
    });
}

function findName(nr, a){
    for(var i=0; i<a.length; i++){
        if(nr==a[i].id){
            return a[i].name;
        }
    }
}

//[{source: {name: "SFO"}, destination: {name: "ATL"}}, {source: {name:"ATL"}, destination: {name: "SFO"}}]
console.log(arr);

Getting expected array using map and filter:

var a = [{id: 1, name:"SFO"}, {id:2, name:"ATL"}];
var b = [{number: 1, sourceId:1, destinationId:2}, {number:2, sourceId:2, destinationId:1}];

var arr = b.map(function(obj){
    return {
        source: { name: a.filter(function(obj2){ if(obj2.id==obj.sourceId) return obj2.name; })[0].name },
        destination: { name: a.filter(function(obj2){ if(obj2.id==obj.destinationId) return obj2.name; })[0].name }
    };
});

//[{source: {name: "SFO"}, destination: {name: "ATL"}}, {source: {name:"ATL"}, destination: {name: "SFO"}}]
console.log(arr);

edited Dec 13, 2016 at 12:05

answered Dec 13, 2016 at 11:29

CroMagnon

1,2047 gold badges21 silver badges32 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

EI-01 Over a year ago

@CrogMagon can this be achieved using map and filter?

EI-01 Over a year ago

@CrogMagon i believe the time complexity would be O(n^2). Its there a way to optimize this?

Nenad Vracar · Accepted Answer · 2016-12-13 11:40:28Z

0

If you have to do this you can use map() and find() but this is very inefficient and you should change your data structure.

var a = [{id: 1, name:"SFO"}, {id:2, name:"ATL"}];
var b = [{number: 1, sourceId:1, destinationId:2}, {number:2, sourceId:2, destinationId:1}];


var result = a.map(function(e) {
  var o = {}
  o.source = {
    name: e.name
  }
  var destB = b.find(function(f) {
    return e.id == f.sourceId
  })
  if (destB) {
    destB = destB.destinationId
    var destName = a.find(function(x) {
      return x.id == destB
    })
    if (destName) {
      destName = destName.name;
      o.destination = {
        name: destName
      }
    }
  }
  return o
})

console.log(result)

answered Dec 13, 2016 at 11:40

Nenad Vracar

122k16 gold badges160 silver badges184 bronze badges

4 Comments

EI-01 Over a year ago

would map and filter be more efficient?

Nenad Vracar Over a year ago

I don't think so, it would be less efficient because find() ends search when it finds first result.

EI-01 Over a year ago

so avoid map and filter?

Nenad Vracar Over a year ago

I this case its better to use find() instead of filter()

Collectives™ on Stack Overflow

How to combine filter and reduce on arrays in javascript

2 Answers 2

2 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related