F# - convert Array to list

Question

I am reading a file into an array like follows (note I know this is bad code):

let filename = if argv.[0] != null then argv.[0] else System.Console.ReadLine()
let data = File.ReadAllLines(filename)

I want to perform an F# map onto the data returned in that above line. My problem is that I can only perform map on n F# list, and not the System.String[] that File.ReadAllLines() returns. Can I convert a standard .Net array into an F# list. I'm sure that I could just read the file differently, or labor through manually copying the array contents to a list, but it would be a lot easier if there was a simple way to do this.

Answer 1

You can use Array.toList to do that.

let data2 = data |> Array.toList

Or you can use List.ofArray

let data2 = data |> List.ofArray

You can also do Array.map instead of List.map and in that case you might not need to map to list at all.

Answer 2

Since File.ReadAllLines returns an array, you can use Array.map on it. It works the same way as List.map .

Another option is Seq.map , since arrays also implement the seq 'a ( IEnumerable<T> ) interface.

As others have pointed out, you can also convert the array to a list using Array.toList or List.ofArray , but be aware that this operation traverses the array and copies it to a list (hence there's a small overhead involved in doing so).