LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox (Kit George)

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

Bill_McC — Wed, 04 Jul 2007 05:49:34 GMT

Should use a StringBuilder instead of String in the Concat method.

Which is kind of interesting becuase how do you use a string builder effectively with the lambda function approach ?

Lambdas : some good, some very bad..

@ Head — Wed, 04 Jul 2007 05:54:27 GMT

One of the new things in Orcas is Lambda functions (or inline functions/BLOCKED EXPRESSION. Although

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

Bill_McC — Wed, 04 Jul 2007 06:05:41 GMT

oh, and although I assume that lambda does work in this case because each item is as String, the CheckListBox items might not be as string, so it's probably safer if the code was

x.ToString & ", " & y.ToString

Also I presume that the code you showed would be reliant on Option Strict Off, as there is no way the compiler could infer the type to be as String becuase the collection is as Object.

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

Klaus Enevoldsen — Wed, 04 Jul 2007 09:21:23 GMT

I'm missing one ingredient: Visual Studio 2008 (Beta2 or Higher). :-)

Anyway it would be better to check the length of the "str" variable in stead of comparing it to an empty string "".

Public Module AggregateModule

<Extension()> Public Function Concat(Of Type)( _

ByVal ie As IEnumerable(Of Type)) As String

Dim str As String = ""

For Each item In ie

If str.Length() > 0 Then str &= ","

str &= item.ToString()

Return str

End Function

End Module

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

Kit George — Wed, 04 Jul 2007 11:12:43 GMT

Agreed on the length check, and agreed on the builder generally. For short concats, builders won't make much difference of course, but if we're building long strings, StringBuilder would be definitely preferred.

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

Ken Getz — Wed, 25 Jul 2007 23:36:14 GMT

This may be less efficient, but it makes me happier (and works with Option Strict On):

<Extension()> Public Function Concat(Of Type)( _

ByVal ie As IEnumerable(Of Type)) As String

Dim items As New List(Of String)

For Each item In ie

items.Add(item.ToString())

Return String.Join(", ", items.ToArray())

End Function

I just hate that "check to ensure you haven't already got an item to avoid the leading comma problem" issue. It just bugs me...

And I keep thinking that I should be able to cast ie As IEnumerable into List(Of String), to avoid adding each item in turn, but I sure can't figure out the syntax.

re: LINQ Cookbook, Recipe 5: Concatenating the selected strings from a CheckedListBox

VBTeam — Thu, 26 Jul 2007 01:58:48 GMT

nice variant, thanks Ken