append rows - which method is faster

[smercurio_fc]

The results are not really that suprising. With method 3 you incur the time hit from having to allocate the array. Even by taking it out, it's not going to be faster in this case because you have to iterate over the rows. The other 2 method do not have this "impediment", so that's why they're faster.

[CoastalMaineBird]

You can answer such questions yourself with a timing tool:

What Time Is It 

[ceties]

Well, I can time the operation. My question now is if there is more efficient way of using the memory preallocation and then replacing the elements (method3) as ppl suggested before.

[smercurio_fc]

Not for your specific case. And that's because Replace Array Subset doesn't take a 2D array as the new element/subarray if the input array is 2D. This means that you need to replace by rows/columns as your method 3 does. In each of your methods the outer for-loop is simply running the same method N times. When you remove this we see that we're left with basically a single operation for the Insert Array method, a few operations for the Build Array method, but a whole loop for the Replace Array Subset method (which has a Build Array inside the loop to boot). This last method will take longer in this specific case.

Preallocation and use of Replace Array Subset is useful as an alternative to using Build Array inside a loop to create an array. This does not mean that it's the most efficient method in all cases. As always, the task to be accomplished dictates which method is the most efficient method.

[ceties]

thanks smercurio. I just wanted to be sure that I didn't overlook something and there is no better way. Thanks