Scala - 将 Array[String] 转换为 Array[Double]
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/28785064/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Scala - convert Array[String] to Array[Double]
提问by Sharadha Jayaraman
I am a newbie to functional programming language and I am learning it in Scala for a University project.
我是函数式编程语言的新手，我正在 Scala 中为大学项目学习它。
This may seem simple, but I am unable to find enough help online for this or a straightforward way of doing this - how can I convert an Array[String] to Array[Double]? I have a CSV file which, when read into the REPL is interpreted as String values (each line of the file has a mix of integer and string values) which would return a type Array[String]. I want to encode the string values with a double/int values to return Array[Double] in order to make the array homogeneous. Is there a straightforward way of doing this? Any guidance will be much appreciated.
这可能看起来很简单，但我无法在网上找到足够的帮助或直接的方法 - 如何将 Array[String] 转换为 Array[Double]？我有一个 CSV 文件，当读入 REPL 时，它被解释为字符串值（文件的每一行都有整数和字符串值的混合），它将返回一个类型 Array[String]。我想用 double/int 值对字符串值进行编码以返回 Array[Double] 以使数组均匀。有没有一种直接的方法来做到这一点？任何指导将不胜感激。
What I have done until now is:
到目前为止我所做的是：
def retrieveExamplesFromFile(fileName : String) : Array[Array[String]] = {
val items = for {
line <- Source.fromFile(fileName).getLines()
entries = line.split(",")
} yield entries
return items.toArray
}
The format of each line (returned as String[]) is so:
每行的格式（以 String[] 形式返回）如下：
[[1.0, 2.0, item1], [5, 8.9, item2],....]
And to convert each line in the CSV file into double array, I only have a psuedo definition drafted so:
并将 CSV 文件中的每一行转换为双数组，我只起草了一个伪定义：
def generateNumbersForStringValues(values : Array[String]) : Array[Double] = {
val line = for(item <- values)
{
//correct way?
item.replace("item1", "1.0")
item.replace("item2", "1.0")
}
return //unable to typecast/convert
}
Any ideas are welcome. Thank you for your time.
欢迎任何想法。感谢您的时间。
回答by Ben Reich
You probably want to use mapalong with toDouble:
您可能想与以下map一起使用toDouble：
values.map(x => x.toDouble)
Or more concisely:
或者更简洁：
values.map(_.toDouble)
And for the fallback for non-double strings, you might consider using the Trymonad (in scala.util):
对于非双字符串的回退，您可以考虑使用Trymonad (in scala.util)：
values.map(x => Try(x.toDouble).getOrElse(1.0))
If you know what each line will look like, you could also do pattern matching:
如果您知道每一行的样子，您还可以进行模式匹配：
values map {
case Array(a, b, c) => Array(a.toDouble, b.toDouble, 1.0)
}
回答by Lodewijk Bogaards
You mean to convert all strings to double with a fallback to 1.0 for all inconvertible strings? That would be:
您的意思是将所有字符串转换为 double 并为所有不可转换的字符串回退到 1.0？那将是：
val x = Array(
Array("1.0", "2.0", "item1"),
Array("5", "8.9", "item2"))
x.map( _.map { y =>
try {
y.toDouble
} catch {
case _: NumberFormatException => 1.0
}
})
回答by Joseph Sawyer
Expanding on @DaunnC's comment, you can use the Tryutility to do this and pattern match on the result so you can avoid calling getor wrapping your result in an Option:
扩展@DaunnC 的评论，您可以使用该Try实用程序来执行此操作并对结果进行模式匹配，这样您就可以避免get将结果调用或包装在Option：
import scala.util.{Try, Success, Failure}
def main = {
val maybeDoubles = Array("5", "1.0", "8.5", "10.0", "item1", "item2")
val convertDoubles = maybeDoubles.map { x =>
Try(x.toDouble)
}
val convertedArray = convertDoubles.map {
_ match {
case Success(res) => res
case Failure(f) => 1.0
}
}
convertedArray
}
This allows you to pattern match on the result of Try, which is always either a Successor Failure, without having to call getor otherwise wrap your results.
这允许您对 的结果进行模式匹配，结果Try始终是 aSuccess或Failure，而无需调用get或以其他方式包装您的结果。
Here is some more information on Try courtesy of Mauricio Linhares: https://mauricio.github.io/2014/02/17/scala-either-try-and-the-m-word.html
以下是 Mauricio Linhares 提供的有关 Try 的更多信息：https: //mauricio.github.io/2014/02/17/scala-either-try-and-the-m-word.html
回答by Xavier Guihot
Scala 2.13introduced String::toDoubleOptionwhich used within a maptransformation, can be associated with Option::getOrElseto safely cast Strings into Doubles:
Scala 2.13引入String::toDoubleOption在map转换中使用的，可以与Option::getOrElse安全地将Strings 转换为Doubles相关联：
Array("5", "1.0", ".", "8.5", "int").map(_.toDoubleOption.getOrElse(1d))
// Array[Double] = Array(5.0, 1.0, 1.0, 8.5, 1.0)
