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How to Concatenate Collections into Strings

I was writing a For…Each loop yesterday to create a comma-delimited string from the properties of objects in a collection (and, thanks to LINQ, I don't write many For…Each loops any more). As I was typing in my code I noticed that the String class's Join method now accepts a collection as one of its parameters. That let me delete my whole For…Each loop because, with this new version of Join, all I have to do is pass the Join method the separator I want between my strings (in this case, a comma) and a collection of strings.

Since the collection I wanted to process was a collection of Customer objects, I did need to include a lambda expression to specify which property on the Customer object I wanted to concatenate (I could also have overridden my Customer's ToString method to return the value I wanted to concatenate). So, in the end, all I needed was this:

Dim res = String.Join(",",  db.Customers.Select(Function(c) c.FirstName)) 

I got back the string "Peter,Jan,Jason…" and so on.

One sad thing: This feature is only available in .NET 4.5. I'm not saying that, all by itself, this feature is a compelling reason to upgrade, but I am now lobbying a little bit harder to get my clients using older versions of .NET to upgrade.

Posted by Peter Vogel on 06/17/2014 at 8:19 AM


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