C# Enumerable ToLookup(IEnumerable, Func, Func)
Description
Creates a Lookup from an IEnumerable according to specified key selector and element selector functions.
Syntax
public static ILookup<TKey, TElement> ToLookup<TSource, TKey, TElement>(
this IEnumerable<TSource> source,
Func<TSource, TKey> keySelector,
Func<TSource, TElement> elementSelector
)/*from w w w . j a va 2 s. com*/
Parameters
TSource- The type of the elements of source.TKey- The type of the key returned by keySelector.TElement- The type of the value returned by elementSelector.source- The IEnumerable to create a Lookup from.keySelector- A function to extract a key from each element.elementSelector- A transform function to produce a result element value from each element.
Example
The following code example demonstrates how to use ToLookup to create a Lookup by using a key selector function and an element selector function.
/*from ww w.ja v a 2s .c o m*/
using System;
using System.Linq;
using System.Collections.Generic;
public class MainClass{
public static void Main(String[] argv){
List<Package> packages =new List<Package>
{ new Package { Company = "A", Weight = 25.2, TrackingNumber = 8L },
new Package { Company = "B", Weight = 18.7, TrackingNumber = 9L },
new Package { Company = "C", Weight = 6.0, TrackingNumber = 2L },
new Package { Company = "D", Weight = 9.3, TrackingNumber = 28L },
new Package { Company = "E", Weight = 33.8, TrackingNumber = 3L } };
ILookup<char, string> lookup = packages
.ToLookup(p => Convert.ToChar(p.Company.Substring(0, 1)),
p => p.Company + " " + p.TrackingNumber);
foreach (IGrouping<char, string> packageGroup in lookup)
{
Console.WriteLine(packageGroup.Key);
foreach (string str in packageGroup)
Console.WriteLine(" {0}", str);
}
}
}
class Package{
public string Company { get; set; }
public double Weight { get; set; }
public long TrackingNumber { get; set; }
}
The code above generates the following result.
