Contains example. We add System.Collections.Generic at the top. The example in the program shows the Contains extension being used on the List type with a case-insensitive search.
Part 1 A string List is constructed. The code adds 3 string literals to the collection's internal array through the Add method.
Part 4 Contains returns a bool. When an element is not found, Contains returns false. We can store the result in an expression.
using System;
using System.Collections.Generic;
using System.Linq;
// Part 1: create List with three elements.
var list = new List<string>();
list.Add("cat");
list.Add("dog");
list.Add("moth");
// Part 2: search for this element.
if (list.Contains("dog"))
{
Console.WriteLine("dog was found");
}
// Part 3: search for this element in any string case.// ... This is the LINQ method with the same name.
if (list.Contains("MOTH", StringComparer.OrdinalIgnoreCase))
{
Console.WriteLine("MOTH was found (insensitive)");
}
// Part 4: this element is not found.
Console.WriteLine(list.Contains("fish"));dog was found
MOTH was found (insensitive)
False
Benchmark. We benchmark the performance of List Contains and a custom for-loop on a small List. Only a few elements are searched by each method.
Version 2 This version uses the Contains method on the List, which reduces the amount of code needed.
Result A custom for-loop was faster. Typically writing a for-loop that does a search is faster than using a built-in method.
using System;
using System.Collections.Generic;
using System.Diagnostics;
class Program
{
/// <summary>/// Custom implementation./// </summary>
static bool ContainsLoop(List<string> list, string value)
{
for (int i = 0; i < list.Count; i++)
{
if (list[i] == value)
{
return true;
}
}
return false;
}
const int _max = 100000000;
static void Main()
{
var list = new List<string>();
list.Add("one");
list.Add("two");
list.Add("three");
list.Add("four");
list.Add("five");
var s1 = Stopwatch.StartNew();
// Version 1: use loop to search a list.
for (int i = 0; i < _max; i++)
{
bool f = ContainsLoop(list, "four");
}
s1.Stop();
var s2 = Stopwatch.StartNew();
// Version 2: use Contains method.
for (int i = 0; i < _max; i++)
{
bool f = list.Contains("four");
}
s2.Stop();
Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
}
}19.22 ns For-loop, string comparisons [ContainsLoop]
54.60 ns Contains method [Contains]
Discussion. System.Linq is included by default in new Console applications in Visual Studio. It will allow you to call a separate Contains generic method on all IEnumerable types.
Warning LINQ extension methods are often slower. They operate on the IEnumerable interface.
Detail The LINQ Contains method accepts 2 parameters (it accepts an IEqualityComparer).
Internals. Contains performs a linear search through the elements, starting with the first element, and uses Equals to check each element value.
Info This is often much slower than a Dictionary. The LINQ method also does a linear search.
A summary. We used the Contains method on List. We saw how this method differs from the LINQ Contains method. The methods are implemented with a forward linear search.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Oct 27, 2023 (edit link).
