Projection in LINQ C# with the Select operator

You can use the Select() extension method in LINQ to create an output of type T from an input sequence of type other than T. Let’s see some examples:

Source data:

string[] bands = { "ACDC", "Queen", "Aerosmith", "Iron Maiden", "Megadeth", "Metallica", "Cream", "Oasis", "Abba", "Blur" , "Chic", "Eurythmics", "Genesis", "INXS", "Midnight Oil", "Kent", "Madness", "Manic Street Preachers", "Noir Desir", "The Offspring", "Pink Floyd", "Rammstein", "Red Hot Chili Peppers", "Tears for Fears", "Deep Purple", "KISS"};

Say you want to collect the lengths of each string in the array:

IEnumerable<int> lengths = bands.Select(b => b.Length);
foreach (int l in lengths)

Select operator simple output

You can also project to a sequence of anonymous objects…:

var customObjects = bands.Select(b => new { Name = b, Length = b.Length });
foreach (var item in customObjects)
	Console.WriteLine("Band name: {0}, length: {1}", item.Name, item.Length);

Select operator extended output

…or to different concrete objects:

public class Band
	public string Name { get; set; }
	public int NameLength { get; set; }
	public string AllCapitals { get; set; }

IEnumerable<Band> bandList = bands.Select(b => new Band() { AllCapitals = b.ToUpper(), Name = b, NameLength = b.Length });
foreach (Band band in bandList)
	Console.WriteLine(string.Concat(band.Name, ", ", band.NameLength, ", ", band.AllCapitals));

Select operator custom object output

An overload of Select() allows us to read an index value:

public class Band
	public string Name { get; set; }
	public int NameLength { get; set; }
	public string AllCapitals { get; set; }
	public int BandIndex { get; set; }

IEnumerable<Band> bandList = bands.Select((b, i) => new Band() { AllCapitals = b.ToUpper(), BandIndex = i + 1, Name = b, NameLength = b.Length });
foreach (Band band in bandList)
	Console.WriteLine(string.Concat(band.BandIndex, ": ", band.Name, ", ", band.NameLength, ", ", band.AllCapitals));

Select operator indexed object output

You can view all LINQ-related posts on this blog here.


About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


A great site

Elliot Balynn's Blog

A directory of wonderful thoughts

Robin Sedlaczek's Blog

Developer on Microsoft Technologies

HarsH ReaLiTy

A Good Blog is Hard to Find

Softwarearchitektur in der Praxis

Wissenswertes zu Webentwicklung, Domain-Driven Design und Microservices

the software architecture

thoughts, ideas, diagrams,enterprise code, design pattern , solution designs

Technology Talks

on Microsoft technologies, Web, Android and others

Software Engineering

Web development

Disparate Opinions

Various tidbits

chsakell's Blog

Anything around ASP.NET MVC,WEB API, WCF, Entity Framework & AngularJS

Cyber Matters

Bite-size insight on Cyber Security for the not too technical.

Guru N Guns's

OneSolution To dOTnET.

Johnny Zraiby

Measuring programming progress by lines of code is like measuring aircraft building progress by weight.

%d bloggers like this: