CODEWITHSUNDEEP
javascript
joeforyou
joeforyou

Reputation: 31

How do I concatenate strings within an array of objects nested inside another array of objects?

Here's the JSON object I'm working with:

var object = {
    "units": [
        { "unitNum": "1", "fuels": [{ "fuelDesc": "Coal" }] },
        { "unitNum": "2", "fuels": [{ "fuelDesc": "Pipeline Natural Gas" }] }
    ]
}

What's the most performative way of concatenating all of the fuelDesc strings into one string, separated by ,?

NOTE: I've simplified the object here. The actual objects is a lot larger so I'm concerned with performance. Also, the fuels array can have more than one item.

The result would be "Coal,Pipeline Natural Gas".

I did this:

var fuelsStr = "";
for (i = 0; i < units.length; i += 1) {
    var mergedFuels = [].concat.apply([], units[i].fuels)
    var unitFuelStr = mergedFuels.map(function (mergedFuels) {
        return mergedFuels["fuelDesc"];
    }).join(",");
    fuelsStr += unitFuelStr;
}

Upvotes: 0

Views: 831

Answers (3)

John Hooper
John Hooper

Reputation: 372

i would use a combination of javascript's reduce and map functions

var object = {
  "units": [{
    "unitNum": "1",
    "fuels": [{
      "fuelDesc": "Coal"
    }]
  }, {
    "unitNum": "2",
    "fuels": [{
      "fuelDesc": "Pipeline Natural Gas"
    }, {
      "fuelDesc": "some fuel"
    }]
  }]
};

var myStr = object.units.reduce(
  (first, second) =>
  first.fuels.map(item =>
    item.fuelDesc)
  .concat(second.fuels.map(item => item.fuelDesc))).join()
  
  console.log(myStr);

I believe this is just about as efficient as you can get, but its been a while since ive done math involving big O so if someone can prove me wrong let me know!

Upvotes: 0

Slai
Slai

Reputation: 22876

For JSON string, the JSON.parse reviver can be used:

a = [], j = '{"units":[{"unitNum":"1","fuels":[{"fuelDesc":"Coal"}]},{"unitNum":"2","fuels":[{"fuelDesc":"Pipeline Natural Gas"}]}]}'

JSON.parse(j, (k, v) => k === "fuelDesc" ? a.push(v) : 0)

console.log(a + '')

For JavaScript object, the JSON.stringify replacer :

a = [], o = {"units":[{"unitNum":"1","fuels":[{"fuelDesc":"Coal"}]},{"unitNum":"2","fuels":[{"fuelDesc":"Pipeline Natural Gas"}]}]}

JSON.stringify(o, (k, v) => k === "fuelDesc" ? a.push(v) : v)

console.log(a + '')

Upvotes: 2

Sajeetharan
Sajeetharan

Reputation: 222582

Based on assumption that you always have one element inside the fuels array. you can use .map and .join together

var myobject = {"units":[{"unitNum": "1","fuels":[{"fuelDesc":"Coal"}]},
{"unitNum": "2","fuels":[{"fuelDesc":"Pipeline Natural Gas"}]}]};

var result = myobject.units.map(function(elem){
    return elem.fuels[0].fuelDesc;
}).join(",");

console.log(result);

Upvotes: 1

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