Duplicate Array item x number of times based off a value inside each array item

Question

I am using javascript and trying to duplicate an array item based off of the number of matches that are inside each item. I believe I need to use arr.map() to accomplish this but am having trouble with the evaluation logic.

So in the example below Item 1 would be duplicated 3 times and Item 2 would be duplicated 1 time. Thanks your help and your time.

My current array looks like:

"cards" = [
    {
        "text": "Item 1"
        "matches": 3
    }
    {
        "text": "Item 2"
        "matches": 1
    }
]

New Array would look like:

"newCards" = [
    {
        "text": "Item 1"
        "matches": 3
    }
    {
        "text": "Item 1"
        "matches": 3
    },
    {
        "text": "Item 1"
        "matches": 3
    },
    {
        "text": "Item 2"
        "matches": 1
    },
    {
        "text": "Item 2"
        "matches": 1
    }
]

attempting to use map function

let cardCounter = 0

let cardMap = cards.map(function (item){
cardCounter++
if (cardCounter < item.matches) {
 // Not really sure what to return here....
 // tried to return
 // return[item, item]
 // this returns an array where the first two keys are arrays and the rest undefined.
}

})

I don't think map is the right tool for the job, unless you intend to return arrays and then flatten the result. — VLAZ
– VLAZ, Commented Oct 15, 2018 at 19:59
Either .forEach() or .reduce() would be more appropriate than .map() — Barmar
– Barmar, Commented Oct 15, 2018 at 20:04
Should the duplicates be copies of the object or multiple references to the same object? — Barmar
– Barmar, Commented Oct 15, 2018 at 20:05
Thanks for you suggestions @barmar they would be exact duplicates of each object — bilcker
– bilcker, Commented Oct 15, 2018 at 20:08
That doesn't really answer my question. References to the same object are exact duplicates. Do you need to be able to modify one of them without affecting the other? — Barmar
– Barmar, Commented Oct 15, 2018 at 20:11

erm410 · Accepted Answer · 2018-10-15 20:18:56Z

1

I don't think map is a good choice as it does one value to one value mapping. If you have lodash available you could use flatMap in which case your return[item, item] idea would work. If not then perhaps use reduce. Something like:

let cardMap = cards.reduce(function (acc, item){
      for (let i = 0; i < item.matches; i++) {
             acc.push(item);
      }
      return acc;
}, []);

edited Oct 15, 2018 at 20:18

answered Oct 15, 2018 at 20:04

erm410

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3 Comments

Barmar Over a year ago

What is item.test, is that a typo for item.text? The example in the question shows that the result should contain objects, not just one property.

bilcker Over a year ago

Thank you this worked. As I ended up pushing the entire object back into the array instead of just the text but all in all it worked. acc.push(item) thanks for your expertise

erm410 Over a year ago

Thanks @Barmar, I've cleaned it up

Marc M. · Accepted Answer · 2018-10-15 20:04:00Z

0

How about this:

var cards = [
    {
        "text": "Item 1",
        "matches": 3
    },
    {
        "text": "Item 2",
        "matches": 1
    }
]

var newCardsArray = [];

cards.forEach(function(element) {
    for(i = 0; i < element.matches; i++) {
        newCardsArray.push(element);
    }
});

console.log(newCardsArray);

answered Oct 15, 2018 at 20:04

Marc M.

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