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)
{
	Console.WriteLine(l);
}

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.

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

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