Linq where clause problem

Question

I thought I'd seen somewhere a while back an example of where clause which called a function that gave a bool result ,and I can't find it again so I'll outline my problem.

I have a collection

Dictionary< string, KeyValuePair < int, int >>  

in which I want to have a query for the string key. On the surface that is simple but unfortunately the string (over which I have no control) is an encoded co-ordinate of a grid cell.

The query is to retrieve entries (as the type of Dictionary) which fall into a certain part of the grid. Placing a function call cells.Where(c => isWithinArea(c.Key, area)) compiles but does not work. The function never gets called.

I would welcome any suggestions to make this work with a minimum of fuss.

Answer 1

The most likely reasons the function is never called would be if the sequence you're "where-ing" has no elements, or you are never invoking the enumerator at all. LINQ is lazy-evaluated, which means none of the expressions you've provided are actually invoked until you start to foreach or ToList().

Answer 2

cells.Keys.Where(key => isWithinArea(key, area))

Answer 3

Thanks for your replies. Yes I did forget the ToList(), silly me. You'd think I know that by now. Then I do a ToDictionary() to the result to conveert it back to a dictionary of the same format so I can access items directly by the key. I'm still trying to make it work in a single line.