Creating nested arrays of set structure

I have an array of objects with named keys as follows:

Array1 [

'town1': 'London', // string
'town2': 'Paris', // string
'distance': 123456, // number
,

'town1': 'Seoul', // string
'town2': 'Tokio', // string
'distance': 654321, // number
,
,,... // Objects with same properties
]


Note that there might be objects without these keys. They should be skipped.

Having all this I want to create a new Array of arrays with 2 objects inside with the following rigid structure:

Array2 [
[ name: 'town1', value: 'distance', name: 'town2'],
[ name: 'town1', value: 'distance', name: 'town2'],
[..., ...], // All other objects with existing town1-town2-distance
]


How one could achieve it in the most efficient and fast way?

[ name: 'London', value: 123456 , name: 'Paris' ]

4 Answers
4

Ok, I want to have my try as well! Why did nobody think about reduce? It's faster than for-loop! And more elegant. IMO at least.

So I've done few tests, and here are results:

And heres the code:

1) Array.prototype.reduce() with Array.prototype.push()

Array.prototype.reduce()

Array.prototype.push()

const array2 = array1.reduce((arr, obj) =>
if (obj.hasOwnProperty('town1') && obj.hasOwnProperty('town2') && obj.hasOwnProperty('value'))
arr.push([ name: obj.town1, value: obj.distance , name: obj.town2 ])


return arr
, )


2) Array.prototype.reduce() with Array.prototype.concat()

Array.prototype.reduce()

Array.prototype.concat()

const array2 = array1.reduce((arr, obj) => (
(obj.hasOwnProperty('town1') && obj.hasOwnProperty('town2') && obj.hasOwnProperty('value'))
? Array.prototype.concat(arr, [[ name: obj.town1, value: obj.distance , name: obj.town2 ]])
: arr
), )


3) Array.prototype.reduce() with spread operator

Array.prototype.reduce()

array2 = array1.reduce((arr, obj) => (
(obj.hasOwnProperty('town1') && obj.hasOwnProperty('town2') && obj.hasOwnProperty('value'))
? [...arr, [ name: obj.town1, value: obj.distance , name: obj.town2 ]]
: arr
), )


4) And @Emueeus go. For-loop with Array.prototype.push()

For-loop

Array.prototype.push()

for (let i = 0; i<array1.length; i++)
if (array1[i].hasOwnProperty('town1') && array1[i].hasOwnProperty('town2') && array1[i].hasOwnProperty('distance'))
array2.push([name:array1[i]['town1'], value: array1[i]['distance'], name: array1[i]['town2']])




Here's the test:
http://jsfiddle.net/4bca0g2u/

performance.now()

MinusFour's solution is almost correct. You'd also want to filter the elements which actually have the keys required:

Array2.filter(obj => obj.hasOwnProperty("town1") &&
obj.hasOwnProperty("town2") &&
obj.hasOwnProperty("distance"))
.map(obj => [ name: obj.town1, value: obj.distance , name: obj.town2 ]);


Is that what you're looking for?

Looks like a single map would work for you.

map

let mustHave = ['town1', 'town2', 'distance'];
Array1.filter(obj => mustHave.every(key => obj.hasOwnProperty(key))
.map(obj => [ name : obj.town1, value: obj.distance, name : obj.town2 ])


Edit: Didn't see that you didn't want to map objects without those keys. The filter takes care of that.

Just one iteration ( O(n) ) using for. It's faster than filter and map (2 iterations) see this https://jsperf.com/mapfiltervsfor/1

for

var array1 = [

'town1': 'London', // string
'town2': 'Paris', // string
'distance': 123456, // number
,

'town1': 'Seoul', // string
'town2': 'Tokio', // string
'distance': 654321, // number

];

var array2 = ;

for(let i = 0; i<array1.length; i++)

if(array1[i].hasOwnProperty('town1') && array1[i].hasOwnProperty('town2') && array1[i].hasOwnProperty('distance'))
array2.push([name:array1[i]['town1'], value: array1[i]['distance'], name: array1[i]['town2']])



console.log(array2)

.map

.sort

.filter

for

for

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