Using Vector Code rather than loop code

[mradulagarwal]

Hi everyone

I am trying to create an array which stores last green candle close value as it occurs. I am able to perfectly achieve this using loop with below code

LastGreenClose = 0;
for( i = 15; i < BarCount; i++ )
{
	if(C[i] > O[i]) 
		LastGreenClose[i] = C[i];
	else
		LastGreenClose[i] = LastGreenClose[i-1];
}

However, I am looking for a more AFL way of doing this using vector processing, as I believe it will be atleast 10X faster. I am trying the following code but it gives undesired result

LastGreenCLose = IIf(C>O, C, Ref(LastGreenCLose, -1);

I know the above line won't work because Ref(x, -1) will just create a new array first, while I am trying to use this array in a recursive sense (created bar by bar sense as in the loop).

Please help me with a vectorised code for achieving the same result as the loop code.
Thanks in advance.

[Tomasz]

Search for ValueWhen function. It does what you need.

There are literally dozens of posts that already cover what you asked for, example:

Doubt when using self referencing

Hi Guys, Just bought Amibroker and getting the hang of AFL. I have a doubt on when you self reference a variable. For Ex: a = (ref(a,-1)) + 2 Generally this would result in an error unless I initialize a[0] and then use for loop for the rest of the array. Is there a work around to this. For Ex. In tradingview they have a simple function called nz() which would erase all null values.

and

Convert Metastock indicator to AFL

This has been covered in my post: Doubt when using self referencing The code presented in original post in this thread is typical example when people don't understand how to write proper vector code. Metastock PREV is classical example of wrong idea being used in even worse way. MS PREV is evil. It causes entire formula to be wrapped in implicit loop causing re-execution that many times as there are bars in the data This makes it run N-times slower where N is number of bars. Even with small 650…

and

http://www.amibroker.com/kb/2014/09/29/debugging-techniques-part-1-exploration/

and ValueWhen will be something like 30-50x faster than loop. Your loop can be replaced by single function call that not only is shorter but also much cleaner than loop and reads like plain English sentence:

"give me the VALUE of Close WHEN Close was higher than Open"

LastGreenCLose = ValueWhen( C > O, C ); // that is easy and straightforward one-liner

So array code is actually easier to write than looping code if you just stop thinking in "obsolete" looping terms and starting thinking on the concept level (what this code actually does).