Count number of unique items in column that meet some criteria

[#1]

Suppose in "Big Class" I'd like a formula that counts the number of unique names of people at or less than the height of the person in the current row.  How can I do that?

I have this:

thisHeight = :height;
Col N Unique( :name, :height <= thisHeight );

I realize the second parameter is the grouping parameter, and it's more intuitive to try to constrain what gets passed into the first parameter, but I haven't had any luck with anything I've tried to this point.

[#2]

The closest built in function that comes to mind is Col Rank( :height, <<tie( "maximum" ) ). The problem is: this counts the total number of rows at or below thisHeight, not the number of unique names. 

Instead, you could try a custom formula, like this: 

thisHeight = :height; //store the current height value

// Build an associative array to collect unique names at or below thisHeight
aa = Associative Array();
For( i = 1, i <= N Rows(), i++,
    If( Column("height")[i] <= thisHeight, 
        aa[Column("name")[i]] = 1  // This only adds to the Associative Array if this is a new, unique name
    )
);

// The number of Items that have been added to the array = number of unique names
N Items( aa )