Builds a new string whose characters are the results of applying the function mapping to each of the characters of the input string and concatenating the resulting strings.

mapping : char -> string

The function to produce a string from each character of the input string.

str : string

The input string.

Returns: string

The concatenated string.

Example

The following samples shows how to interspace spaces in a text

 let input = "Stefan says: Hi!"

 input |> String.collect (sprintf "%c ")

Example

How to show the ASCII representation of a very secret text

 "Secret" |> String.collect (fun chr -> int chr |> sprintf "%d ")

Returns a new string made by concatenating the given strings with separator sep, that is a1 + sep + ... + sep + aN.

sep : string

The separator string to be inserted between the strings of the input sequence.

strings : seq<string>

The sequence of strings to be concatenated.

Returns: string

A new string consisting of the concatenated strings separated by the separation string.

Example

 let input1 = ["Stefan"; "says:"; "Hello"; "there!"]

 input1 |> String.concat " "  // evaluates "Stefan says: Hello there!"

 let input2 = [0..9] |> List.map string

 input2 |> String.concat ""    // evaluates "0123456789"
 input2 |> String.concat ", "  // evaluates "0, 1, 2, 3, 4, 5, 6, 7, 8, 9"

 let input3 = ["No comma"]

 input3 |> String.concat ","   // evaluates "No comma"

Tests if any character of the string satisfies the given predicate.

predicate : char -> bool

The function to test each character of the string.

str : string

The input string.

Returns: bool

True if any character returns true for the predicate and false otherwise.

Example

Looking for uppercase characters

 open System

 "Yoda" |> String.exists Char.IsUpper  // evaluates true

 "nope" |> String.exists Char.IsUpper  // evaluates false

Builds a new string containing only the characters of the input string for which the given predicate returns "true".

Returns an empty string if the input string is null

predicate : char -> bool

A function to test whether each character in the input sequence should be included in the output string.

str : string

The input string.

Returns: string

The resulting string.

Example

Filtering out just alphanumeric characters

 open System

 let input = "0 1 2 3 4 5 6 7 8 9 a A m M"

 input |> String.filter Uri.IsHexDigit  // evaluates "123456789aA"

Example

Filtering out just digits

 open System

 "hello" |> String.filter Char.IsDigit  // evaluates ""

Tests if all characters in the string satisfy the given predicate.

predicate : char -> bool

The function to test each character of the string.

str : string

The input string.

Returns: bool

True if all characters return true for the predicate and false otherwise.

Example

Looking for lowercase characters

 open System

 "all are lower" |> String.forall Char.IsLower  // evaluates false

 "allarelower" |> String.forall Char.IsLower    // evaluates true

Builds a new string whose characters are the results of applying the function mapping to each index from 0 to count-1 and concatenating the resulting strings.

count : int

The number of strings to initialize.

initializer : int -> string

The function to take an index and produce a string to be concatenated with the others.

Returns: string

The constructed string.

Example

Enumerate digits ASCII codes

 String.init 10 (fun i -> int '0' + i |> sprintf "%d ")

Applies the function action to each character in the string.

action : char -> unit

The function to be applied to each character of the string.

str : string

The input string.

Example

Printing the ASCII code for each characater in the string

 let input = "Hello"
 input |> String.iter (fun c -> printfn "%c %d" c (int c))

 H 72
 e 101
 l 108
 l 108
 o 111

Applies the function action to the index of each character in the string and the character itself.

action : int -> char -> unit

The function to apply to each character and index of the string.

str : string

The input string.

Example

Numbering the characters and printing the associated ASCII code for each characater in the input string

 let input = "Hello"
 input |> String.iteri (fun i c -> printfn "%d. %c %d" (i + 1) c (int c))

 1. H 72
 2. e 101
 3. l 108
 4. l 108
 5. o 111

Returns the length of the string.

str : string

The input string.

Returns: int

The number of characters in the string.

Example

Getting the length of different strings

 String.length null   // evaluates 0
 String.length ""     // evaluates 0
 String.length "123"  // evaluates 3

Builds a new string whose characters are the results of applying the function mapping to each of the characters of the input string.

mapping : char -> char

The function to apply to the characters of the string.

str : string

The input string.

Returns: string

The resulting string.

Example

Changing case to upper for all characters in the input string

 open System

 let input = "Hello there!"

 input |> String.map Char.ToUpper  // evaluates "HELLO THERE!"

Builds a new string whose characters are the results of applying the function mapping to each character and index of the input string.

mapping : int -> char -> char

The function to apply to each character and index of the string.

str : string

The input string.

Returns: string

The resulting string.

Example

 input |> String.mapi (fun i c -> (i, c))

Returns a string by concatenating count instances of str.

count : int

The number of copies of the input string will be copied.

str : string

The input string.

Returns: string

The concatenated string.

Example

 "Do it!" |> String.replicate 3