For example:
import scala.collection.mutable.ArrayBuffer
val times = ArrayBuffer(Some("Last week"), Some("Last month"), Some("Last year"))
How do I find the index of Last year/Last month/... in this array buffer?
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3 Answers
You can use indexOf
times.indexOf(Some("Last month")) // returns 1
Update
You can convert the times ArrayBuffer[Option[String]] into a ArrayBuffer[String] via
val l = times.map(_.getOrElse("")) // ArrayBuffer("Last week", "Last month", ...)
And then you can search for the strings
l.indexOf("Last month")
3 Comments
sk1007
How to convert in list (Remove Some )for eg: List("Last week", "Last month". "Last year")
Kevin Meredith
Understood that you answered his question, Till. But, calling
times.map(_.getOrElse("") adds an additional walk of the list - certainly not necessary for what you're trying to do.
Till Rohrmann
You're right @KevinMeredith. This is not the most efficient solution. If you want to convert the list from
List[Option[String]] to List[String] and find the index of the element with a certain value in one pass, then you can combine it in the map function. However, you basically double the operations of your map function, which will lead to the same complexity as with the two pass approach (assuming that you have only few cache misses).You can use indexOf or lastIndexOf. Example:
times indexOf ( Some( "Last year" ) )
Also you can use indexWhere or lastIndexWhere. For example:
times indexWhere { _.get == "Last year" }
Comments
Perhaps not as efficient as indexOf, but more readable, I'd argue:
scala> times.zipWithIndex.find(
{ case (value, _) => value == Some("Last week") }
).map(_._2)
res7: Option[Int] = Some(0)
Or, using flatMap:
scala> times.zipWithIndex.flatMap {
| case (value, index) => value match {
| case Some("Last week") => ArrayBuffer(index)
| case _ => Nil
| }
| }
res2: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(0)
1 Comment
kira
I could not use the indexOf approach. I used this approach as my object in the ArrayBuffer was not simple String - but a complex one. I used one of the attributes to find the object and zipWithIndex helped getting the index.