Change index in array.map

Question

I have a variable of the form:

var data=[
{
    start:22,
    end: 8
},
{
    start:60,
    end: 43       
},
{
    start: 35,
    end: 55
},
{
    start:25,
    end:40
}
];

I want to map it to look like this

var newData = { 22:8, 60:43, 35:55, 25:40};

Is this possible? I mainly just want to use the start numbers as a key to access the end numbers without using search. I have tried to do this:

 var mapData = data.map(function(data){
  var x = {};
  x[data.start]=data.end;
  return x;
});

but it gives: 0 : {22: 8} 1 : {60: 43} 2 : {35: 55} 3 : {25: 40} which means i have to use 0, 1,2, 3 as indices.

please add a valid result.

Nina Scholz
– Nina Scholz

2017-11-07 09:04:54 +00:00
Commented Nov 7, 2017 at 9:04 — Nina Scholz
– Nina Scholz, Commented Nov 7, 2017 at 9:04
newData is not a valid object.

gurvinder372
– gurvinder372

2017-11-07 09:05:55 +00:00
Commented Nov 7, 2017 at 9:05 — gurvinder372
– gurvinder372, Commented Nov 7, 2017 at 9:05
Did you mean { 22:8, 60:43, 35:55, 25:40 }?

nnnnnn
– nnnnnn

2017-11-07 09:06:16 +00:00
Commented Nov 7, 2017 at 9:06 — nnnnnn
– nnnnnn, Commented Nov 7, 2017 at 9:06
impossible you cant write like "{8}"

Hemant Rajpoot
– Hemant Rajpoot

2017-11-07 09:06:36 +00:00
Commented Nov 7, 2017 at 9:06 — Hemant Rajpoot
– Hemant Rajpoot, Commented Nov 7, 2017 at 9:06
@nnnnnn Yes I meant that, i'll edit to say this.

Nightshade
– Nightshade

2017-11-07 09:08:35 +00:00
Commented Nov 7, 2017 at 9:08 — Nightshade
– Nightshade, Commented Nov 7, 2017 at 9:08

Nina Scholz · Accepted Answer · 2017-11-07 09:13:03Z

4

Only Array#map does not work in this case, because without post processing, you get a single array with objects. You need to combine all objects into a single object.

With Object.assign and spread syntax ..., you get a single array with all properties from the objects in the array.

var data = [{ start: 22, end: 8 }, { start: 60, end: 43 }, { start: 35, end: 55 }, { start: 25, end: 40 }],
    result = Object.assign(...data.map(({ start, end }) => ({ [start]: end })));
    
console.log(result);

edited Nov 7, 2017 at 9:13

answered Nov 7, 2017 at 9:07

Nina Scholz

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1 Comment

Nightshade Over a year ago

Thanks a lot Nina. I was not aware of the spread syntax, since I'm still a beginner to javascript.

Faly · Accepted Answer · 2017-11-07 09:12:52Z

3

You can use array.reduce:

var data=[
{
    start:22,
    end: 8
},
{
    start:60,
    end: 43       
},
{
    start: 35,
    end: 55
},
{
    start:25,
    end:40
}
];

var res = data.reduce((m, o) => { 
  m[o.start] = o.end; 
  return m;
}, {});

console.log(res);

answered Nov 7, 2017 at 9:12

Faly

13.4k2 gold badges21 silver badges39 bronze badges

1 Comment

Nightshade Over a year ago

Thank you, I wasn't aware of these methods.

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