小编aku*_*eck的帖子

我刚刚开始使用F#并试图了解典型的idoms和有效的思考和工作方式.

手头的任务是将制表符分隔文件简单转换为以逗号分隔的文件.典型的输入行将如下所示:

let line = "@ES#    01/31/2006 13:31:00 1303.00 1303.00 1302.00 1302.00 2514    0"

我开始使用这样的循环代码:

// inFile and outFile defined in preceding code not shown here

for line in File.ReadLines(inFile) do
    let typicalArray = line.Split '\t'
    let transformedLine = typicalArray |> String.concat ","   
    outFile.WriteLine(transformedLine)

然后我用一个Regex.Replace()替换了split/concat操作对:

for line in File.ReadLines(inFile) do   
    let transformedLine = Regex.Replace(line, "\t",",")
    outFile.WriteLine(transformedLine)

现在,最后,用管道替换了循环:

File.ReadLines(inFile)
    |> Seq.map  (fun x -> Regex.Replace(x, "\t", ","))
    |> Seq.iter (fun y -> outFile.WriteLine(y))

  // other housekeeping code below here not shown …

我有一个包含两列,文本和计数的CSV文件.目标是从这里转换文件:

some text once,1
some text twice,2
some text thrice,3

对此:

some text once,1
some text twice,1
some text twice,1
some text thrice,1
some text thrice,1
some text thrice,1

重复每一行计数次数并将计数分布在那么多行上.

在我看来,这似乎是Seq.unfold的一个很好的候选者,在我们读取文件时生成了额外的行.我有以下生成器功能:

let expandRows (text:string, number:int32) =
    if number = 0 
    then None
    else
        let element = text                  // "element" will be in the generated sequence
        let nextState = (element, number-1) // threaded state replacing looping 
        Some (element, nextState)

FSI产生以下函数签名:

val expandRows : text:string * number:int32 -> (string * (string * …