How do I get the index of an object in a For Each...Next loop?

Question

I'm using the following syntax to loop through a list collection:

For Each PropertyActor As JCPropertyActor In MyProperty.PropertyActors

    i = IndexOf(PropertyActor)
Next

How do I get the index of the current object within the loop? I'm using IndexOf(PropertyActor) but this seems inefficient as it searches the collection when I already have the object available!

Answer 1

just initialize an integer variable before entering the loop and iterate it...

Dim i as Integer 
For Each PropertyActor As JCPropertyActor In MyProperty.PropertyActors
    i++
Next

Answer 2

Add an index variable that you increase yourself for each iteration?

Answer 3

AFAIK since this pulls the object out of the collection, you would have to go back to the collection to find it.

If you need the index, rather than using a for each loop, I would just use a for loop that went through the indices so you know what you have.

Answer 4

It might be easiest to just keep a separate counter:

i = 0
For Each PropertyActor As JCPropertyActor In MyProperty.PropertyActors
    ...
    i = i + 1
Next

As an aside, Python has a convenient way of doing this:

for i, x in enumerate(a):
    print "object at index ", i, " is ", x

Answer 5

An index doesn't have any meaning to an IEnumerable, which is what the foreach construct uses. That's important because foreach may not enumerate in index order, if your particular collection type implements IEnumerable in an odd way. If you have an object that can be accessed by index and you care about the index during an iteration, then you're better off just using a traditional for loop:

for (int i=0;i<MyProperty.PropertyActors.Length;i++)
{
    //...
}

Answer 6

You could use the "FindIndex" method.

MyProperty.PropertyActors.FindIndex(Function(propActor As JCPropertyActor) propActor  = JCPropertyActor)

But inside of a for each loop that seems like alot of extra overhead, and seems like the same resulting problem as the "IndexOf" method. I suggest using old fashioned index iteration. This way you have your index and your item.

Dim PropertyActor As JCPropertyActor
For i As Integer = 0 To MyProperty.PropertyActors.Count - 1
    PropertyActor = MyProperty.PropertyActors.Item(i)
Next

Answer 7

Index is only available on List objects, so PropertyActor is not a List object and for that does not have an index, what you can do however is get the index of the List object that contains the current propertyActor object like:

i = MyProperty.PropertyActors.IndexOf(PropertyActor)