LINQ sample: select typed objects from a list

Question

I have

Dim objectsList as List(Of Object) = GetAllObjects()

' Filter from Objects just Persons '
Dim peopleList as List(Of Person) = ???

What is the most efficient and effective LINQ expression to do it?

EDIT

1 Dim selectedObjects As List(Of Object) = GetAllObjects()
2 Dim selectedPeople As IEnumerable(Of Person)= selectedObjects.OfType(Of Person)
3 Dim people As List(Of Person) = selectedPeople.ToList()

Error on 3:

Value of type 'System.Collections.Generic.List(Of System.Collections.Generic.IEnumerable(Of Person))' cannot be converted to 'System.Collections.Generic.List(Of Person)'.

Jon Skeet · Accepted Answer · 2011-07-07 12:55:49Z

4

Sounds like you want Enumerable.OfType():

Dim peopleList as List(Of Person) = objectsList.OfType(Of Person)().ToList()

answered Jul 7, 2011 at 12:55

Jon Skeet

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2 Comments

serhio Over a year ago

in fact, you obtain an IEnumerable, not a List(Of), but pretty cool enough! ) Thank you )

Marc Gravell Over a year ago

@serhio the ToList() does that last step

jason · Accepted Answer · 2011-07-07 13:12:17Z

1

The most effecient approach is to filter at the point of origin (for example, at the point of database query, for example), not once we have the objects in memory, but:

Dim peopleList as List(Of Person) = objectsList.OfType(Of Person)().ToList()

or in C# (note this is identical once compiled):

var peopleList = objectsList.OfType<Person>().ToList();

edited Jul 7, 2011 at 13:12

jason

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answered Jul 7, 2011 at 12:56

Marc Gravell

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Comments

Viv · Accepted Answer · 2011-07-07 12:56:27Z

0

In C# it would be

ObjectList.OfType<Person>()

VB .Net would be something similar

answered Jul 7, 2011 at 12:56

Viv

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