list 查找列表中元素的索引scala
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Finding the index of an element in a list scala
提问by yAsH
How do I find the index of an element in a Scala list.
如何在 Scala 列表中找到元素的索引。
val ls = List("Mary", "had", "a", "little", "lamb")
I need to get 3 if I ask for the index of "little"
如果我要求“小”的索引，我需要得到 3
回答by DaoWen
scala> List("Mary", "had", "a", "little", "lamb").indexOf("little")
res0: Int = 3
You might try reading the scaladoc for Listnext time. ;)
回答by Rok Kralj
If you want to search by a predicate, use .indexWhere(f):
如果要按谓词搜索，请使用.indexWhere(f)：
val ls = List("Mary", "had", "a", "little", "lamb","a")
ls.indexWhere(_.size <= 3)
This returns 1, since "had" is the first word with at most 3 letters.
这将返回 1，因为“had”是第一个最多包含 3 个字母的单词。
回答by Jatin
If you want list of all indices containing "a", then:
如果您想要包含“a”的所有索引的列表，则：
val ls = List("Mary", "had", "a", "little", "lamb","a")
scala> ls.zipWithIndex.filter(_._1 == "a").map(_._2)
res13: List[Int] = List(2, 5)
