system.Random.Sample snippet

samples/snippets/fsharp/VS_Snippets_CLR_System/system.Random.Sample/FS/sample.fs

@@ -0,0 +1,128 @@
+// <Snippet1>
+open System
+
+// This derived class converts the uniformly distributed random
+// numbers generated by base.Sample() to another distribution.
+
+type RandomProportional() =
+    inherit Random()
+
+    // The Sample method generates a distribution proportional to the value
+    // of the random numbers, in the range [0.0, 1.0].
+    override _.Sample() =
+        sqrt (base.Sample())
+
+    override this.Next() =
+        this.Sample() * float Int32.MaxValue
+        |> int
+
+let [<Literal>] rows = 4
+let [<Literal>] cols = 6
+let [<Literal>] runCount = 1000000
+let [<Literal>] distGroupCount = 10
+
+let intGroupSize =
+    (float Int32.MaxValue + 1.0) / float distGroupCount
+
+let randObj = RandomProportional()
+
+printfn """
+The derived RandomProportional class overrides the Sample method to 
+generate random numbers in the range [0.0, 1.0]. The distribution 
+of the numbers is proportional to their numeric values. For example, 
+numbers are generated in the vicinity of 0.75 with three times the 
+probability of those generated near 0.25."""
+
+printfn "\nRandom doubles generated with the NextDouble() method:\n"
+
+// Generate and display [rows * cols] random doubles.
+for _ = 1 to rows do 
+    for _ = 1 to cols do
+        printf $"{randObj.NextDouble(),12:F8}"
+    printfn ""
+
+printfn "\nRandom integers generated with the Next() method:\n"
+// Generate and display [rows * cols] random integers.
+for _ = 1 to rows do 
+    for _ = 1 to cols do
+        printf $"{randObj.Next(),12}"
+    printfn ""
+
+printfn $"""
+To demonstrate the proportional distribution, 
+{runCount:N0} random 
+integers and doubles are grouped into {distGroupCount} equal value ranges. This 
+is the count of values in each range:
+"""
+
+printfn $"""{"Integer Range",21}{"Count",10}{"Double Range",20}{"Count",10}"""
+printfn $"""{"-------------",21}{"-----",10}{"------------",20}{"-----",10}"""
+
+// Generate random integers and doubles, and then count them by group.
+let intCounts = 
+    Array.init runCount (fun _ -> 
+        (randObj.Next() |> float) / float intGroupSize
+        |> int )
+    |> Array.countBy id
+    |> Array.map snd
+
+let realCounts = 
+    Array.init runCount (fun _ -> 
+        randObj.NextDouble() * float intGroupSize
+        |> int )
+    |> Array.countBy id
+    |> Array.map snd
+
+// Display the count of each group.
+for i = 1 to distGroupCount - 1 do 
+    Console.WriteLine(
+        "{0,10}-{1,10}{2,10:N0}{3,12:N5}-{4,7:N5}{5,10:N0}",
+        (int)((float)i * intGroupSize),
+        (int)((float)(i + 1) * intGroupSize - 1.0),
+        intCounts.[i],
+        ((float)i) / (float)distGroupCount,
+        ((float)(i + 1)) / (float)distGroupCount,
+        realCounts.[i])
+
+(*
+This example of Random.Sample() displays output similar to the following:
+
+    The derived RandomProportional class overrides the Sample method to
+    generate random numbers in the range [0.0, 1.0). The distribution
+    of the numbers is proportional to the number values. For example,
+    numbers are generated in the vicinity of 0.75 with three times the
+    probability of those generated near 0.25.
+
+    Random doubles generated with the NextDouble() method:
+
+        0.59455719  0.17589882  0.83134398  0.35795862  0.91467727  0.54022658
+        0.93716947  0.54817519  0.94685080  0.93705478  0.18582318  0.71272428
+        0.77708682  0.95386216  0.70412393  0.86099417  0.08275804  0.79108316
+        0.71019941  0.84205103  0.41685082  0.58186880  0.89492302  0.73067715
+
+    Random integers generated with the Next() method:
+
+        1570755704  1279192549  1747627711  1705700211  1372759203  1849655615
+        2046235980  1210843924  1554274149  1307936697  1480207570  1057595022
+        337854215   844109928  2028310798  1386669369  2073517658  1291729809
+        1537248240  1454198019  1934863511  1640004334  2032620207   534654791
+
+    To demonstrate the proportional distribution, 1,000,000 random
+    integers and doubles are grouped into 10 equal value ranges. This
+    is the count of values in each range:
+
+            Integer Range     Count        Double Range     Count
+            -------------     -----        ------------     -----
+            0- 214748363    10,079     0.00000-0.10000    10,148
+    214748364- 429496728    29,835     0.10000-0.20000    29,849
+    429496729- 644245093    49,753     0.20000-0.30000    49,948
+    644245094- 858993458    70,325     0.30000-0.40000    69,656
+    858993459-1073741823    89,906     0.40000-0.50000    90,337
+    1073741824-1288490187   109,868     0.50000-0.60000   110,225
+    1288490188-1503238552   130,388     0.60000-0.70000   129,986
+    1503238553-1717986917   149,231     0.70000-0.80000   150,428
+    1717986918-1932735282   170,234     0.80000-0.90000   169,610
+    1932735283-2147483647   190,381     0.90000-1.00000   189,813
+*)
+// </Snippet1>
+

xml/System/Random.xml

@@ -1143,6 +1143,7 @@ Each element of the span of bytes is set to a random number greater than or equa
 
  :::code language="cpp" source="~/samples/snippets/cpp/VS_Snippets_CLR_System/system.Random.Sample/cpp/sampleex.cpp" id="Snippet1":::
  :::code language="csharp" source="~/samples/snippets/csharp/VS_Snippets_CLR_System/system.Random.Sample/CS/sample.cs" interactive="try-dotnet" id="Snippet1":::
+ :::code language="fsharp" source="~/samples/snippets/fsharp/VS_Snippets_CLR_System/system.Random.Sample/FS/sample.fs" id="Snippet1":::
  :::code language="vb" source="~/samples/snippets/visualbasic/VS_Snippets_CLR_System/system.Random.Sample/VB/sample.vb" id="Snippet1":::
 
  ]]></format>