Not too difficult. Just increment the counter of the for
loop by 3 each iteration and then offset the indexer to get the batch of 3 at a time:
for(int i=0; i < theData.Length; i+=3)
{
var item1 = theData[i];
var item2 = theData[i+1];
var item3 = theData[i+2];
}
If the length of the array wasn't garuanteed to be a multiple of three, you would need to check the upper bound with theData.Length - 2
instead.