Delete from array?
BlitzMax Forums/BlitzMax Programming/Delete from array?
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| (Tried to locate existing posts on this but found nothing.) Is it possible to delete items from an array? Example: arr:int[1,2,3,4,5] How to remove the 3? Any help would be appreciated. |
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| Check "slices" in the documentation, that should help you do what you are after. |
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| Slices don't work with multi-dimensional arrays, only single-dimension.... So the answer is probably "Can't be done" (unless you create a new array and copy the desired contents over) |
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I think what he meant was:Local arr:Int[]=[1,2,3,4,5] arr=arr[..2]+arr[3..] For ct=0 To 3 Print arr[ct] Next |
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| Ah. Makes sense, I was misinterpreting the question. |
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| Isn't this pretty inefficient, because you are allocating 2 new chunks of memory (slow) when all you really need is one memcopy (instant)? |
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| Yes.. but I didn't put a tonne of thought into it either :) 3 kids running around... you know ;) |
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| I don't think there is presently any other way of doing this. A memcopy will mess up GC for an array of objects. There should be something like this: arr=arr[..3..] or: arr=arr[..3..5..] |
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| If he's just storing int's then using a bank with memory copy would be quicker (I think) |
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| If he's just storing int's then using a bank with memory copy would be quicker (I think) Only as long as you are remembering that your "bank" will be virtually shorter - since you are shifting a whole block down a bit. What would you do with the now empty end bit? (other than setting the values to 0, I suppose). |
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| or set the first int as the length |
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| You can use memcopy with object arrays, but it will mess up the GC, of course, so don't do it. |
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| What is this array being used for? Perhaps a linked list would be more appropriate? I'd personally swap the 3 with the end 5, then either resize downwards one, or have a variable to keep track of the "usable length". Assuming the order of elements in the array was unimportant.. |
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I suggest trying the self-optimizing arrays that I sort of invented ... basically like this:Local MyArray:Int[50] Local Space:Int=50 Local Items:Int=0 'Add an item... If Items=Space then ResliceTheArrayToMakeItBigger() 'and add to Space MyArray[Items]=Whatever Items:+1 'Remove item 3 from an array, assuming it already contains 12 items... 'Space will = 50 'Items will = 12 MyArray[3]=MyArray[Items-1] Items:-1 So basically when you add to the array you add after the previous item, at the end. When you remove something from the array, you copy the end item and overwrite the removed item with it, then decrease the number of items. So long as you don't need your array to be sorted it'll work. If you need your array to stay sorted, I suggest associating it with an array of indexes. |
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| Even if you do a conventional slice, you still need an extra array to keep track of the indexes, if you want to be able to directly remove items. And you need another array with the real and fake indexes sorted the opposite way. Does anyone have something like this written already? |
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