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System.Comparison<T> F# Snippets (#7537)
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‎samples/snippets/fsharp/VS_Snippets_CLR/List`1_SortComparison/fs/fs.fsproj‎

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="source.fs" />
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</ItemGroup>
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</Project>

‎samples/snippets/fsharp/VS_Snippets_CLR/List`1_SortComparison/fs/source.fs‎

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// <Snippet1>
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open System
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let compareDinosByLength (x: string) (y: string) =
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match x with
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| null when isNull y ->
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// If x is null and y is null, they're equal.
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0
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| null ->
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// If x is null and y is not null, y is greater.
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-1
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| _ when isNull y->
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// If x is not null and y is null, x is greater.
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1
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| _ ->
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// If x is not null and y is not null, compare the lengths of the two strings.
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let retval = x.Length.CompareTo y.Length
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if retval <> 0 then
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// If the strings are not of equal length, the longer string is greater.
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retval
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else
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// If the strings are of equal length, sort them with ordinary string comparison.
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x.CompareTo y
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let display list =
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printfn ""
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for s in list do
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if isNull s then
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printfn "(null)"
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else
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printfn $"\"%s{s}\""
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let dinosaurs = ResizeArray()
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dinosaurs.Add "Pachycephalosaurus"
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dinosaurs.Add "Amargasaurus"
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dinosaurs.Add ""
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dinosaurs.Add null
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dinosaurs.Add "Mamenchisaurus"
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dinosaurs.Add "Deinonychus"
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display dinosaurs
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printfn "\nSort with generic Comparison<string> delegate:"
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dinosaurs.Sort compareDinosByLength
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display dinosaurs
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// This code example produces the following output:
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//
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// "Pachycephalosaurus"
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// "Amargasaurus"
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// ""
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// (null)
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// "Mamenchisaurus"
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// "Deinonychus"
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//
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// Sort with generic Comparison<string> delegate:
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//
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// (null)
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// ""
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// "Deinonychus"
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// "Amargasaurus"
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// "Mamenchisaurus"
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// "Pachycephalosaurus"
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// </Snippet1>

‎samples/snippets/fsharp/VS_Snippets_CLR_System/system.comparison`1/fs/comparisont1.fs‎

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// <Snippet1>
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open System
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type CityInfo =
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{ City: string
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Country: string
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Population: int }
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static member CompareByName city1 city2 =
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String.Compare(city1.City, city2.City)
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static member CompareByPopulation city1 city2 =
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city1.Population.CompareTo city2.Population
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static member CompareByNames city1 city2 =
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String.Compare(city1.Country + city1.City, city2.Country + city2.City)
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let display cities =
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printfn $"""{"City",-20} {"Country",-25} {"Population",10}"""
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for city in cities do
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printfn $"{city.City,-20} {city.Country,-25} {city.Population,10:N0}"
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printfn ""
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let NYC = { City = "New York City"; Country = "United States of America"; Population = 8175133 }
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let Det = { City = "Detroit"; Country = "United States of America"; Population = 713777 }
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let Paris = { City = "Paris"; Country = "France"; Population = 2193031 }
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let cities = [| NYC; Det; Paris |]
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// Display ordered array.
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display cities
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// Sort array by city name.
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Array.Sort(cities, CityInfo.CompareByName)
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display cities
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// Sort array by population.
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Array.Sort(cities, CityInfo.CompareByPopulation);
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display cities
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// Sort array by country + city name.
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Array.Sort(cities, CityInfo.CompareByNames);
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display cities
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// The example displays the following output:
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// City Country Population
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// New York City United States of America 8,175,133
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// Detroit United States of America 713,777
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// Paris France 2,193,031
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//
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// City Country Population
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// Detroit United States of America 713,777
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// New York City United States of America 8,175,133
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// Paris France 2,193,031
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//
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// City Country Population
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// Detroit United States of America 713,777
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// Paris France 2,193,031
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// New York City United States of America 8,175,133
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//
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// City Country Population
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// Paris France 2,193,031
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// Detroit United States of America 713,777
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// New York City United States of America 8,175,133
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// </Snippet1>

‎samples/snippets/fsharp/VS_Snippets_CLR_System/system.comparison`1/fs/fs.fsproj‎

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<Project Sdk="Microsoft.NET.Sdk">
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<PropertyGroup>
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<OutputType>Exe</OutputType>
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<TargetFramework>net6.0</TargetFramework>
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</PropertyGroup>
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<ItemGroup>
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<Compile Include="comparisont1.fs" />
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</ItemGroup>
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</Project>

‎xml/System/Comparison`1.xml‎

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:::code language="cpp" source="~/samples/snippets/cpp/VS_Snippets_CLR/List`1_SortComparison/cpp/source.cpp" id="Snippet1":::
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:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR/List`1_SortComparison/cs/source.cs" interactive="try-dotnet" id="Snippet1":::
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:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR/List`1_SortComparison/fs/source.fs" id="Snippet1":::
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:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR/List`1_SortComparison/vb/source.vb" id="Snippet1":::
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The following example uses the <xref:System.Comparison%601> delegate to sort the elements of a collection of `CityInfo` objects. `CityInfo` is an application-defined class that contains information about a city and its population. The example defines three methods, `CompareByName`, `CompareByPopulation`, and `CompareByNames`, that offer three different ways of ordering the `CityInfo` objects. Each method is assigned to the `comparison` argument of the <xref:System.Array.Sort%60%601%28%60%600%5B%5D%2CSystem.Comparison%7B%60%600%7D%29?displayProperty=nameWithType> method.
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:::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.comparison`1/cs/comparisont1.cs" interactive="try-dotnet" id="Snippet1":::
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:::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.comparison`1/fs/comparisont1.fs" id="Snippet1":::
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:::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.comparison`1/vb/comparisont1.vb" id="Snippet1":::
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]]></format>

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