how can i find a key in a map based on a pattern matching in scala

I want to find a key in a map that is similar to a sp开发者_高级运维ecific text. should I use for loop or is there a more elegant way?

The direct translation of your question is map.keys.find(_.matches(pattern)) which given a map, gets they keys and finds the first key that matches the regexp pattern.

val map = Map("abc" -> 1, "aaa" -> 2, "cba" -> 3)
map.keys.find(_.matches("abc.*"))
// Some(abc)
map.keys.find(_.matches("zyx"))
// None

A loop may be counter productive if you don't want to scan all keys.

Suppose you have some regular expression which you wish to match on:

val RMatch = """\d+:(\w*)""".r

And a function, which takes the matched group for the regex, and the value in the map

def f(s: String, v: V): A

Then you can match on the regex and collect the value of the function:

map collectFirst { case (RMatch(_), v) => f(txt, v) }

If you just wanted the value...

map collectFirst { case (RMatch(txt), v) => v }

Note: the implementation of this method effects a traversal on the map, in case that is not what you were desiring

It depends on the pattern and the map's underlying implementation. If the map is a HashMap, then it can only give you an exact match against a key, so you can't do anything better than loop over its keys. If the map is a SortedMap and you know the beginning of the text you're looking for, then you can use the range method to obtain a part of the map based on the pattern, and loop over that range.

It really depends on what you mean by 'similar to' and 'text'. If you are using English words you could use the Soundex algorithm (http://en.wikipedia.org/wiki/Soundex) to give you a code for each word and use that as a hash key, collecting all the words with the same Soundex value together in a list. If you want to do full text matching then it's a lot more complicated and you need to use techniques such as Inverted Indexes (http://en.wikipedia.org/wiki/Inverted_index). In that case you'd be best looking at something pre-written such as Apache Lucene (http://lucene.apache.org/java/docs/) which gives you much more besides simple inverted indexes. Lucene is written in Java, so it is directly usable from Scala.