Convert Examples (String, Int, Array)
This page was last reviewed on Dec 22, 2023.
Dot Net Perls
Convert. Conversions between types can be done in a variety of ways in F#. As an example, we can convert a String an Int with a parsing method. This is a more efficient representation of the data.
For simple conversions, a cast like downcast or upcast is sufficient. For parsing a string, we use Int32.TryParse. For arrays, Seq.asArray and toArray are helpful.
downcast, upcast
Convert string to int. To convert a number in a string into an int, we use the Int32.TryParse. Other types like Int64 also have equivalent parsing methods.
Start We must declare a "parsed value" storage location. We decorate this value (result) with the mutable keyword so it can be changed.
Info The first argument is the string. The second one is the storage variable for the parsed value—we pass it as a reference.
Return When TryParse returns true, we enter the if-block. In this case the parse was successful and the result was assigned.
open System // This string contains an Int32. let test = "100" // Stores the parsed value from TryParse. let mutable result = 0 // If TryParse succeeds, value is stored in result. if Int32.TryParse(test, &result) then // Print the parsed value. printfn "%A" result
Seq.ofArray, toArray. A Seq is powerful: we can use many methods on it, like "where" or "map." With Seq.ofArray we treat an array as a sequence.
Here We use the Seq.where method on an array (which is being treated as a sequence).
Result We remove elements that do not start with "C" and convert the result back into a string array with Seq.toArray.
// This is a string array. let candies = [|"chocolate"; "sugar"; "cookie"|] // Use Seq.ofArray to convert to a seq. // ... Use Seq.toArray to convert seq to a string array. let firstLetterC = Seq.ofArray candies |> Seq.where (fun x -> x.StartsWith("c")) |> Seq.toArray printfn "%A" firstLetterC
[|"chocolate"; "cookie"|]
Option to int. In F# many methods return an option. We can convert the option to a value by testing it with IsSome. If an inner value exists, we then access it with Value.
let numbers = [10; 20; 30] // The tryFind method returns an option containing an int. let result = List.tryFind (fun x -> x >= 15) numbers // See if the option has a value. if result.IsSome then // Convert the option into an Int. let number = result.Value printfn "%d" number
Bool to int. Sometimes we have a bool and want to convert it to an int—usually 1 for true and 0 for false. An inline if-expression can be used to do this.
let code = true // Convert bool to 1 or 0. let number = if code then 1 else 0 printfn "%A" code printfn "%A" number
true 1
With conversions, we change types of our data so that is it more useful. Ints are more effective when dealing with numeric data than strings containing digits.
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 Dec 22, 2023 (edit).
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