As a general rule, you should not modify a collection that your are looping over, only the items inside of that collection.  The problem with removing items inside of a for each loop is that it changes the collection that is being looped and interferes with the list count and iteration location.

###Common solutions are to:

1. Loop through the collection backwards so interferences with the iterator won't impact the execution
2. Create a new collection so you can modify one collection and loop over another.

###Loop Backwards:

Here's an extension method that takes in a `Collection(Of T)` (you could use a `List(Of T)`, but the list class already exposes a [`RemoveAll`][List.RemoveAll] method which basically does this same thing).  
We'll loop backwards and check the validity of each item in the collection based on the passed in lambda function.  If it matches, then we'll remove it.



    <Extension()>
    Public Sub RemoveEach(Of T)(ByRef col As Collection(Of T),
                                ByVal match As Func(Of T, Boolean))
        For i = col.Count - 1 To 0 Step -1
            If match(col(i)) Then col.RemoveAt(i)
        Next
    End Sub

Then use like this:



    Dim col = New Collection(Of Integer)({1, 2, 3, 4}.ToList)
    col.RemoveEach(Function(i) (i Mod 2) = 0)
    'Produces list of 1 & 3

###Create New Collection:

It is more efficient to keep track of the collection index and remove items using `RemoveAt` instead of `Remove` which takes an object and then checks the rest of the collection for matches against that object.  However, if you really wanted a way to process removing items within a For Loop, you could call `ToList` on the original collection, thereby creating a new list.  Then, you can loop over the new list to find items that need to be removed from the original.  Whenever you find an object, you can safely remove it from the original collection, because it is not currently being enumerated over.


    <Extension()>
    Public Sub RemoveEachObject(Of T)(ByRef col As Collection(Of T), 
                                      ByVal match As Func(Of T, Boolean))
        For Each o As T In col.ToList()
            If match(o) Then col.Remove(o)
        Next
    End Sub

For more info, check out this great [answer to Remove from a List<T> within a 'foreach' loop][answer].

[List.RemoveAll]: http://msdn.microsoft.com/en-us/library/wdka673a(v=vs.110).aspx
[answer]: https://stackoverflow.com/a/9381864/1366033

I have a generic list that I'm removing items out of using `List.Remove(Object)`. I have been removing items but whenever I get to the fifth item I'm removing it fails and does not remove it from the list. It doesn't seem to matter what I'm removing but everytime I try to remove five items it fails on the fifth item. 

What could be causing this? Looking at the documentation for `List(Of T).Remove`, it doesn't specify what algorithm they're using to remove the item. 


Removing items from a List(Of t) in vb.net failing

In order to allow short circuiting if the duplicate exists early in the list, you can add a [`HashSet<T>`][HashSet] and check the return value of its `.Add` method.  

By using `.Any` you can short circuit the enumeration as soon as you find a duplicate.

Here's a LINQ extension method in both C# and VB:  

### CSharp:



    public static bool ContainsDuplicates<T>(this IEnumerable<T> enumerable)
    {
        var knownKeys = new HashSet<T>();
        return enumerable.Any(item => !knownKeys.Add(item));
    }

### Visual Basic:



    <Extension>
    Public Function ContainsDuplicates(Of T)(ByVal enumerable As IEnumerable(Of T)) As Boolean
        Dim knownKeys As New HashSet(Of T)
        Return enumerable.Any(Function(item) Not knownKeys.Add(item))
    End Function

**Note**: to check if there are *no* duplicates, just change `Any` to `All`

[HashSet]: http://msdn.microsoft.com/en-us/library/bb359438(v=vs.110).aspx

Requirement: In an unsorted List, determine if a duplicate exists.  The typical way I would do this is an n-squared nested loop.  I'm wondering how others solve this.  Is there an elegant, high performance method in Linq?  Something generic that takes a lambda or a comparer would be nice. 

C# Determine Duplicate in List

Like [Slaks pointed out](https://stackoverflow.com/a/6727960/1366033), you can use `Contains` on an `enumerable` collection.  But I think readability suffers.  I don't care if some list ***contains*** my variable; I want to know if my variable is ***in*** some list.  


You can wrap contains in an extension method like so:

```vb
Imports System.Runtime.CompilerServices
Module ExtensionMethods

    <Extension()> _
    Public Function [In](Of T)(ByVal item As T, ByVal ParamArray range() As T) As Boolean
        Return range.Cast(Of T).Contains(item)
    End Function

End Module
```

Then call like this:

```vb
If ToStatus.In("1CE","2TL","2PM") Then
```

I just want to know if there's an approach in VB.NET that can find if a specific value exist on a list or something which can use in my If-else condition. What I'm doing now is to use this:

    If ToStatus = "1CE" Or ToStatus = "2TL" Or ToStatus = "2PM" Then
        'Do something
    Else
        'Do something
    End If

This works fine, but how if I have hundreds of string to compare to `ToStatus` in the future? It will be a nightmare! Now, if such functionality exists, how can I add "And" and "Or" in the statement? 

Thanks in advance!


VB.NET If-Else in List

Following suit from the suggestions here, I added an extension method to return a list of the selected items using LINQ for any type that Inherits from [<code>System.Web.UI.WebControls.<b>ListControl</b></code>][ListControl]. 

Every `ListControl` object has an [`Items`][ListControl.Items] property of type [`ListItemCollection`][ListItemCollection].  `ListItemCollection` exposes a collection of [`ListItems`][ListItems], each of which have a `Selected` property.

###C Sharp:



    public static IEnumerable<ListItem> GetSelectedItems(this ListControl checkBoxList)
    {
        return from ListItem li in checkBoxList.Items where li.Selected select li;
    }

###Visual Basic:



    <Extension()> _
    Public Function GetSelectedItems(ByVal checkBoxList As ListControl) As IEnumerable(Of ListItem)
        Return From li As ListItem In checkBoxList.Items Where li.Selected
    End Function

Then, just use like this in either language:

    myCheckBoxList.GetSelectedItems()

[ListControl]: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listcontrol(v=vs.110).aspx
[ListControl.Items]: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listcontrol.items(v=vs.110).aspx
[ListItemCollection]: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listitemcollection(v=vs.110).aspx
[ListItems]: http://msdn.microsoft.com/en-us/library/system.web.ui.webcontrols.listitem(v=vs.110).aspx

I have a CheckBoxList like this:



    <asp:CheckBoxList ID="CBLGold" runat="server" CssClass="cbl">
        <asp:ListItem Value="TGJU"> TG </asp:ListItem>
        <asp:ListItem Value="GOLDOZ"> Gold </asp:ListItem>
        <asp:ListItem Value="SILVEROZ"> Silver </asp:ListItem>
        <asp:ListItem Value="NERKH"> NE </asp:ListItem>
        <asp:ListItem Value="TALA"> Tala </asp:ListItem>
        <asp:ListItem Value="YARAN"> Sekeh </asp:ListItem>
    </asp:CheckBoxList>

Now I want to get the value of the selected items from this CheckBoxList using foreach, and put the values into a list.

How to get values of selected items in CheckBoxList with foreach in ASP.NET C#?

If you can't change the markup as skelly suggested, you'll have to also override the `display` property back to `list-item`, so you're CSS should look like this:



    footer nav ul.nav > li {
      margin-left: 40px;
      list-style-type: disc;
      display: list-item
    }

### Demo in Stack Snippets





    footer nav ul.nav > li {
      margin-left: 40px;
      list-style-type: disc;
      display: list-item
    }



    <link href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" rel="stylesheet"/>

    <footer>
      <nav>
        <ul class='nav navbar-nav'>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
        </ul>
      </nav>
    </footer>



---

There's still a lot of other CSS styles that would be affecting the list type.  If you want to remove them all, and if you can run javascript on the page, you can just remove the classes with jQuery like this:



    $("footer nav ul.nav.navbar-nav").removeClass("nav navbar-nav");

### Demo in Stack Snippets





    $("footer nav ul.nav.navbar-nav").removeClass("nav navbar-nav");



    footer nav ul.nav > li {
      margin-left: 40px;
      list-style-type: disc;
      display: list-item
    }



    <link href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" rel="stylesheet"/>
    <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>

    <footer>
      <nav>
        <ul class='nav navbar-nav'>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
          <li><a href='#'>Home</a></li>
        </ul>
      </nav>
    </footer>

I am having difficulties restoring the bullet points in a Bootstrap navigation list. My markup is generated by WordPress but the general idea is:

    <nav>
        <ul class='nav navbar-nav'>
            <li><a href='#'>Home</a></li>
            <li><a href='#'>Home</a></li>
            <li><a href='#'>Home</a></li>
            <li><a href='#'>Home</a></li>
        </ul>
    </nav>

I've looked through the styles Bootstrap has applied to what is basically a list, and I can't figure out what is removing the list-style which was originally there.

I tried to set things back to the default by using the below, but this hasn't worked.

    footer nav ul.nav > li {
	    list-style-type:disc;
    }

I am hoping there are any Bootstrap wizards out there who can help me resolve this issue. 