Count unique values until particular value encountered

First post, sorry if I don't explain this well.

I'm trying to count the number of unique participants in each conference that we have had over the last few months, and I'm having trouble getting a formula that I can copy through a whole column.

So in excel speak I'm trying to count the number of unique non-numerical values in column D until a particular non-numerical value(in this case "(blank)") is encountered. This formula needs to occur when there is any value in a third column, in this case column B. The current formula that I have is as follows:

=IF(B16<> "",COUNTA(D16:INDEX($D16:D$2222,MATCH(TRUE,($D17:D$2222= "(blank)"),0))),"")

This counts the number of values until we reach "(blank)", but I need to find the number of UNIQUE values. My question is how do I count only the unique values until "(blank)" is reached?

Thanks for any help.

Hope this works:

				expected
date	name	configured name	number of connections	Number of Unique Connections
(blank)	(blank)	(blank)
1 April 2016	3800 - DAI	Madison DAI-BHS	6	3
		Chicago Deportation Court
		Chicago Deportation Court
		Madison DAI-BHS
		Fox Lake AD-DAI
		Fox Lake AD-DAI
		(blank)
	3801 DAI	Chicago Deportation Court	3	3
		Madison DAI-BHS
		New Lisbon AD-DAI
		(blank)

"(blank)" is an actual text entry.

Worked perfectly, thanks Tony.

It turns out that it occurred when the value was encountered. I changed to "none" and I'm getting the numbers I was looking for. I am still curious why that was happening though.

It turns out that it occurred when the value "none" surrounded by angle brackets was encountered. I changed it to "none" without the brackets and I'm getting the numbers I was looking for. I am still curious why that was happening though.