Fastest way to loop through an object array and get specific keys

Question

Say I have this array:

Dogs = [
    {Name: 'Sparky', OwnerID: 1},
    {Name: 'Pooch', OwnerID: 2},
    {Name: 'Sneak', OwnerID: 1}
]

What is the fastest way for me to do this:

dogNames = Dogs.map(element => element.Name);

I was just wondering if there is something like this:

dogNames = Dogs[...Name];

What's wrong with Dogs.map(element => element.Name)? You could do Dogs.map(({Name})=> Name) but that's not much of an improvement. The syntax you're proposing is not possible — adiga
– adiga, Commented Jan 25, 2019 at 9:30
@adiga Well I feel like these is something like [...] to use? @NinaScholz that was just an example... — Freddy Bonda
– Freddy Bonda, Commented Jan 25, 2019 at 9:32
Are the names unique? Why don't you just create an associative array/object? Get rid of the array altogether and just create one large object. Then its just Dogs['Sparky'], where your object would change to {'Sparky':1,'Pooch':2,'Sneak':1} — SPlatten
– SPlatten, Commented Jan 25, 2019 at 9:32
Possible duplicate of Pure For vs. ES6 Map | Which one to choose? — Dez
– Dez, Commented Jan 25, 2019 at 9:33

Nina Scholz · Accepted Answer · 2019-01-25 09:37:55Z

1

You could take a closure over the wanted key an map the result of only a single property.

const only = k => o => o[k];

var dogs = [{ Name: 'Sparky', OwnerID: 1 }, { Name: 'Pooch', OwnerID: 2 }, { Name: 'Sneak', OwnerID: 1 }],
    dogNames = dogs.map(only('Name'));
    
console.log(dogNames);

answered Jan 25, 2019 at 9:37

Nina Scholz

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2 Comments

SPlatten Over a year ago

If you measure the time from creating the array, converting it to a map then performing the look up compared to referencing an object instead of an array I think the results will be very clear....I don't think converting an array to a map is going to offer much of an increase in performance.

Nina Scholz Over a year ago

in sense of performance you are right. in sense of writing code, not.

Davi · Accepted Answer · 2019-01-25 09:47:28Z

It depends on what you mean by saying "fastest". Do you mean execution time? Fastest to type? Easiest to understand?

When "fastest to type" and "easiest to understand" is what you mean, then I'd rather say something like array.map(x => x.prop) is probably the fastest. You might find a shorter way to type it besides removing the variable and property names, but I can't think of one.

In terms of execution time, most people believe that using loops is the fastest way:

let names = [];
for (let i = 0; i < dogs.length; i += 1) {
  names[i] = dogs[i].Name;
}

Personally, I avoid loops whenever possible and stick with map, filter, reduce – to be honest, mainly because for most projects my execution time is more expensive than the execution time of my script.

Anyway, deciding that is up to you.

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