Back to basics; for-loops, arrays/vectors/lists, and optimization

Question

I was working on some code recently and came across a method that had 3 for-loops that worked on 2 different arrays.

Basically, what was happening was a foreach loop would walk through a vector and convert a DateTime from an object, and then another foreach loop would convert a long value from an object. Each of these loops would store the converted value into lists.

The final loop would go through these two lists and store those values into yet another list because one final conversion needed to be done for the date.

Then after all that is said and done, The final two lists are converted to an array using ToArray().

Ok, bear with me, I'm finally getting to my question.

So, I decided to make a single for loop to replace the first two foreach loops and convert the values in one fell swoop (the third loop is quasi-necessary, although, I'm sure with some working I could also put it into the single loop).

But then I read the article "What your computer does while you wait" by Gustav Duarte and started thinking about memory management and what the data was doing while it's being accessed in the for-loop where two lists are being accessed simultaneously.

So my question is, what is the best approach for something like this? Try to condense the for-loops so it happens in as little loops as possible, causing multiple data access for the different lists. Or, allow the multiple loops and let the system bring in data it's anticipating. These lists and arrays can be potentially large and looping through 3 lists, perhaps 4 depending on how ToArray() is implemented, can get very costy (O(n^3) ??). But from what I understood in said article and from my CS classes, having to fetch data can be expensive too.

Would anyone like to provide any insight? Or have I completely gone off my rocker and need to relearn what I have unlearned?

Thank you

Answer 1

The best approach? Write the most readable code, work out its complexity, and work out if that's actually a problem.

If each of your loops is O(n), then you've still only got an O(n) operation.

Having said that, it does sound like a LINQ approach would be more readable... and quite possibly more efficient as well. Admittedly we haven't seen the code, but I suspect it's the kind of thing which is ideal for LINQ.