Javascript: modify value deep in array

Question

What is the most effective way to modify deep value in multidimensional array?

I have following json:

[
  {"name":"Series 1","data":[
    {"x":1506470700,"y":null},
    {"x":1506499200,"y":null},
    {"x":1506499500,"y":483981},
    {"x":1506499800,"y":504588},
    {"x":1506500100,"y":502926},
    {"x":1506500400,"y":501161},
    {"x":1506500700,"y":506453}]
  },{"name":"Series 2","data":[
    {"x":1506470700,"y":null},
    {"x":1506499200,"y":null},
    {"x":1506499500,"y":-490671},
    {"x":1506499800,"y":-495593},
    {"x":1506500100,"y":-512765},
    {"x":1506500400,"y":-479475},
    {"x":1506500700,"y":-531689}]
  }
]

I'd like to multiply x values by 1000. I can process it using this code for example:

arrayFromJson.forEach((series) => {
    series.data.forEach((dataSet) => {
        dataSet.x *= 1000;
    });
});

But I was wondering whether there isn't more effective/elegant way to do it.

"better" is highly subjective. I don't see anything wrong with your current solution. — robertklep
– robertklep, Commented Sep 27, 2017 at 8:54

Faly · Accepted Answer · 2017-09-27 08:58:20Z

2

Use array map:

var arr = [{"name":"Series 1","data":[{"x":1506470700,"y":null},{"x":1506499200,"y":null},{"x":1506499500,"y":483981},{"x":1506499800,"y":504588},{"x":1506500100,"y":502926},{"x":1506500400,"y":501161},{"x":1506500700,"y":506453}]},{"name":"Series 2","data":[{"x":1506470700,"y":null},{"x":1506499200,"y":null},{"x":1506499500,"y":-490671},{"x":1506499800,"y":-495593},{"x":1506500100,"y":-512765},{"x":1506500400,"y":-479475},{"x":1506500700,"y":-531689}]}];

arr.map(it => {
    it.data = it.data.map(dt => { dt.x = dt.x * 1000 ; return dt;})
});

console.log(arr);

answered Sep 27, 2017 at 8:58

Faly

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1 Comment

Keith Over a year ago

The OP's forEach doesn't generate new arrays, a map here is an overhead that's not required.

cyr_x · Accepted Answer · 2017-09-27 09:09:19Z

1

Your solution is totally fine, but keep in mind that you're mutating the original array, which could potentially cause some side-effects.

For an immutable solution use Array.prototype.map and Object.assign:

var data = [{"name":"Series 1","data":[{"x":1506470700,"y":null},{"x":1506499200,"y":null},{"x":1506499500,"y":483981}]}];

var changedData = data.map(series => {
    return Object.assign({}, series, {
      data: series.data.map(dataSet => { 
        return Object.assign({}, dataSet, { x: dataSet.x * 1000 });
      })
    });
});

console.log(data);
console.log(changedData);

answered Sep 27, 2017 at 9:09

cyr_x

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1 Comment

simPod Over a year ago

Why to use Object.assign instead of =?

Nina Scholz · Accepted Answer · 2017-09-27 09:04:12Z

0

You could write it a bit shorter, without some parentheses and curly brackets. But you need still nested iterations.

arrayFromJson.forEach(series => series.data.forEach(dataSet => dataSet.x *= 1000));

answered Sep 27, 2017 at 9:04

Nina Scholz

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Comments

Massimiliano Janes · Accepted Answer · 2017-09-27 09:12:15Z

0

premising that your current code is perfectly ok, on es6, a ( possibly faster and more readable ) variant could be

for( let series of arrayFromJson )
  for( let data of series.data )
    data.x *= 1000;

on es<6, 'for in' will work too ( given that you don't need ordered traversal, but provided those arrays have no extra own prop ... )

answered Sep 27, 2017 at 9:12

Massimiliano Janes

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