[amibroker] How to exclude symbols?

["trb0428" <trbrowne@xxxxxxxxxxx>]

I am trying to create an indicator that will calculate the percentage 
of stocks within an industry that are trading above their 50 day 
moving average. 

My problem is if there is a stock in the list that has a short 
trading history, say only trading for 200 days, the entire indicator 
is limited by this short symbol. How can I exclude stocks that fail 
to meet a minimum number of bars in my formula below? I do not want 
to use ATC for this. Thanks.

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summing = 0;
list = CategoryGetSymbols( categoryIndustry, IndustryID(0) ); 

for( i = 0; ( symbol = StrExtract( list, i ) ) != ""; i++ )
{
FC = Foreign( symbol, "C" );
VarSet("C"+i, MA(FC,50)); 
VarSet("S"+i, IIf(FC > MA(FC,50),1,0)); 
summing = summing + VarGet("S"+i);
Plot(VarGet("C"+i),"C"+i,colorWhite,styleLine); 
}
ratio = (summing / i) * 100;

Plot(ratio, "%stocks > 50 DMA", colorBrightGreen, styleLine | 
styleThick);

_N( Title = "# stocks = " + i + " # above 50DMA = " + summing  );