Filter nodelist

Hello everyone,

I have an XML document that contains a few 'product' elements with 'id'
attributes. Because I have to operate on these products a few times I
build a variable that just takes all products with the expression
'descendant::product'. Sometimes I have to iterate over all products.
But that is not all I do with the list. My problem: I have to get the
count of all products from this node-list that have the same id like a
certain product in the list  and that's position in the node-list is
lower. Example:

[product id="A",
 product id="B",
 product id="C",
 product id="B",
 product id="B",  <-
 product id="D",
 product id="E"]

So if I have the product at position 5 the result of the count should be
2, because of the products at position 2 and 4 with the same id.

Any ideas? Thanks.


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