CODEWITHSUNDEEP
c#linq
IceCreamBoi23
IceCreamBoi23

Reputation: 419

Linq select values from multiple lists inside a list

I have a list of lists that contain IntPtr variables like this

var testList = new List<List<IntPtr>>();

I'm trying to selectIntPtr variables from the lists where the size of the list is greater than 0 and the IntPtr does not equal IntPtr.Zero using Linq

I have tried the following

var pointers = testList.Where(list => list.Count > 0)
                       .SelectMany(pointer => pointer != IntPtr.Zero);

What exactly am I doing wrong and how could I modify this statement to get it to work as intended?

Upvotes: 1

Views: 1609

Answers (1)

Ousmane D.
Ousmane D.

Reputation: 56433

Currently, you're passing a predicate to the SelectMany which is not what it expects; instead what it expects is a Func<List<IntPtr>, IEnumerable<IntPtr>> where List<IntPtr> is the input list and IEnumerable<IntPtr> is the value returned upon the function invocation.

SelectMany will then take each nested IEnumerable<IntPtr> and collapse it into a single IEnumerable<IntPtr>.

As well as that, you're also attempting to use the != operator on a sequence (List<IntPtr>) represented by pointer which will not work.

Rather what you should do is first collapse the nested sequencs via SelectMany and then apply the predicate via a Where clause:

var pointers = testList.Where(list => list.Count > 0) // IEnumerable<List<IntPtr>>
                       .SelectMany(list => list) // IEnumerable<IntPtr>
                       .Where(pointer => pointer != IntPtr.Zero); // IEnumerable<IntPtr>

On another note, you don't even need the first Where clause as it can simply be:

var pointers = testList.SelectMany(list => list) // IEnumerable<IntPtr>
                       .Where(pointer => pointer != IntPtr.Zero); // IEnumerable<IntPtr>

Upvotes: 3

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