how do i use the second expression to select only those with ID from the first?
var list1= from x in objects select x.id;
results=results.Where(r=>r.id== ???? )
I want the results to be only those with id from listA
tia
EDIT:i stand corrected, there was another issue causing problem which i will ask about separately.
A bit of a guess (haven't tried running it), but:
var filteredResults = from obj in objects
join result in results on obj.id equals result.id
select result;
Note that this should replace both the lines of code you have in your question.
Like so...
results.Where(r=>list1.Contains(r.id))
results = results.Where(r => list1.Contains(r.id));
If you want some performance (list.Contains() has an O(n) complexity) you could go with
var ids = objects.ToDictionary(o => o.id);
results.Where(o => ids.ContainsKey(o.id));
Maybe you want this then?
results.Where(r=> objects.Any(o => o.id == r.id) )
If You always need only the first element's ID , You can store it to variable and use it to lambda expression
var results= from x in objects select x.id;
int firstID = results.First().id ;
results=results.Where(r=>r.id== firstID )
Or, use directly like this:
var results= from x in objects select x.id;
results=results.Where(r=>r.id== results.First().id )
