On Tuesday, 16 February 2021 at 06:03:50 UTC, H. S. Teoh wrote:
It depends on what your goal is. Do you want to permanently
remove the items from the array? Or only skip over some items
while iterating over it? For the latter, see
std.algorithm.iteration.filter.
The array itself is read only, so it'll have to be an array of
pointers/indexes.
For the former, you can use the read-head/write-head algorithm:
keep two indices as you iterate over the array, say i and j: i
is for reading (incremented every iteration) and j is for
writing (not incremented if array[i] is to be deleted). Each
iteration, if j < i, copy array[i] to array[j]. At the end of
the loop, assign the value of j to the length of the array.
Example:
int[] array = ...;
size_t i=0, j=0;
while (i < array.length)
{
doSomething(array[i]);
if (!shouldDelete(array[i]))
j++;
if (j < i)
array[j] = array[i];
i++;
}
array.length = j;
Basically, the loop moves elements up from the back of the
array on top of elements to be deleted. This is done in tandem
with processing each element, so it requires only traversing
array elements once, and copies array elements at most once for
the entire loop. Array elements are also read / copied
sequentially, to maximize CPU cache-friendliness.
T
This is most likely ideal for what i'm trying to
do.(resizes/removes will probably have to propagate to other
arrays)
The only problem is that it does not work with the first element
but i could always just handle the special case on my own.[1]
I'll probably use .filter or an equivalent for an initial first
pass and this algorithm for the rest, thank you both!
[1] https://run.dlang.io/is/f9p29A (the first element is still
there, and the last element is missing. both occur if the first
element didn't pass the check.)
