Find the first element that satisfies condition X in a Seq
If you're confident at least one will format will succeed:
formats.view.map{format => Try(format.parse(str)).toOption}.filter(_.isDefined).head
If you want to be a bit safer:
formats.view.map{format => Try(format.parse(str)).toOption}.find(_.isDefined)
Try
was introduced in Scala 2.10.
A view
is a type of collection that computes values lazily. It will apply the code within the Try
to only as many items in the collection as is necessary to find the first one that is defined. If the first format
applies to the string, then it won't try to apply the remaining formats to the string.
You should use find
method on sequences. Generally you should prefer built-in methods, because they might be optimised for a specific sequence.
Console println List(1,2,3,4,5).find( _ == 5)
res: Some(5)
That is, to return first SimpleDateFormat that match:
val str = "1903 January"
val formats = List("MMM yyyy", "yyyy MMM", "MM yyyy", "MM, yyyy")
.map(new SimpleDateFormat(_))
formats.find { sdf =>
sdf.parse(str, new ParsePosition(0)) != null
}
res: Some(java.text.SimpleDateFormat@ef736ccd)
To return first date that has being processed:
val str = "1903 January"
val formats = List("MMM yyyy", "yyyy MMM", "MM yyyy", "MM, yyyy").map(new SimpleDateFormat(_))
val result = formats.collectFirst {
case sdf if sdf.parse(str, new ParsePosition(0)) != null => sdf.parse(str)
}
or use lazy collection:
val str = "1903 January"
val formats = List("MMM yyyy", "yyyy MMM", "MM yyyy", "MM, yyyy").map(new SimpleDateFormat(_))
formats.toStream.flatMap { sdf =>
Option(sdf.parse(str, new ParsePosition(0)))
}.headOption
res: Some(Thu Jan 01 00:00:00 EET 1903)
This prevents the unnecessary evaluations.
formats.collectFirst{ case format if Try(format.parse(str)).isSuccess => format.parse(str) }
The number of evaluations of the parse
method is number of tries + 1.