Many Copies of Filtered Array

So I have an array of items, we’ll make it Strings for the example but they’re actually custom objects:

let original = ["apple1", "apple2", "banana1", "banana2", "carrot1", "carrot2", "donut1", "donut2"]

and then I filter the array to only get the “1” foods:

let filtered = original.filter { $0.contains("1") }

Then I want to get a random element from my filtered array and remove it when I do:

let randomIndex = filtered.getRandomIndex // returns a random index in the array
let randomElement = filtered[randomIndex]
filtered.remove(at: randomIndex)

Then when the filtered array contains no more data, I want to reset it back to its original state.

Option 1 is to create three arrays and reset the filtered array when it’s empty:

// original - all strings
// filtered - filtered strings
// ogFiltered - original set of filtered strings

if filtered.count == 0 {
    filtered = ogFiltered

Option 2 is to refilter the original array when filtered is empty:

if filtered.count == 0 {
    filtered = original.filter { $0.contains("1") }

So my question is, which is the better way to do this? Is it better/worse to have more arrays or more computations? Thanks!

More computations and less use of memory, unless it’s too slow.
If it was a huge list with 100,000 items, and you filter it down to 19, I would hang on to that. If you filter it down to 99,000, I would not hang on to that.
If the source might have have changed, I would re-filter it every time, unless you want it to be the same filtered result every time, then I would hang on to it.
It depends. :slight_smile:

1 Like

Thanks @sgerrard!

The filtered array is around the same size as the original array, so I will refilter each time. And the computation time seems pretty quick, since the object contains only string properties.

Thanks for your insight!

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