Seq.iter<'T> Function (F#)
Applies the given function to each element of the collection.
Namespace/Module Path: Microsoft.FSharp.Collections.Seq
Assembly: FSharp.Core (in FSharp.Core.dll)
// Signature:
Seq.iter : ('T -> unit) -> seq<'T> -> unit
// Usage:
Seq.iter action source
Parameters
action
Type: 'T ->unitA function to apply to each element of the sequence.
source
Type: seq<'T>The input sequence.
Exceptions
Exception |
Condition |
|---|---|
Thrown when the input sequence is null. |
Remarks
This function is named Iterate in compiled assemblies. If you are accessing the function from a language other than F#, or through reflection, use this name.
Example
The following example illustrates the use of Seq.iter.
printf "Seq.iter: "
Seq.iter (fun (a,b) -> printf "(%d, %d) " a b) (seq { for i in 1..5 -> (i, i*i) })
Seq.iter: (1, 1) (2, 4) (3, 9) (4, 16) (5, 25)
The following example illustrates the use of Seq.iter to work with CSV (Comma-Separated Value) files.
// Write a test file
System.IO.File.WriteAllLines(@"test.csv", [| "Desmond, Barrow, Market Place, 2";
"Molly, Singer, Band, 12" |]);
/// This function builds an IEnumerable<string list> object that enumerates the CSV-split
/// lines of the given file on-demand
let CSVFileEnumerator(fileName) =
// The function is implemented using a sequence expression
seq { use sr = System.IO.File.OpenText(fileName)
while not sr.EndOfStream do
let line = sr.ReadLine()
let words = line.Split [|',';' ';'\t'|]
yield words }
// Now test this out on our test file, iterating the entire file
let test = CSVFileEnumerator(@"test.csv")
printfn "-------Enumeration 1------";
test |> Seq.iter (string >> printfn "line %s");
// Now do it again, this time determining the numer of entries on each line.
// Note how the file is read from the start again, since each enumeration is
// independent.
printfn "-------Enumeration 2------";
test |> Seq.iter (Array.length >> printfn "line has %d entries");
// Now do it again, this time determining the numer of entries on each line.
// Note how the file is read from the start again, since each enumeration is
// independent.
printfn "-------Enumeration 3------";
test |> Seq.iter (Array.map (fun s -> s.Length) >> printfn "lengths of entries: %A")
-------Enumeration 1------ line System.String[] line System.String[] -------Enumeration 2------ line has 8 entries line has 7 entries -------Enumeration 3------ lengths of entries: [|7; 0; 6; 0; 6; 5; 0; 1|] lengths of entries: [|5; 0; 6; 0; 4; 0; 2|]
Platforms
Windows 8, Windows 7, Windows Server 2012, Windows Server 2008 R2
Version Information
F# Core Library Versions
Supported in: 2.0, 4.0, Portable