[Assorted-commits] SF.net SVN: assorted: [430] scala-commons/trunk/src/commons/Collections. scala

[<yan...@us...>]

Revision: 430
          http://assorted.svn.sourceforge.net/assorted/?rev=430&view=rev
Author:   yangzhang
Date:     2008-02-14 18:31:34 -0800 (Thu, 14 Feb 2008)

Log Message:
-----------
added: separateHeads, groupByHeaders, multimap, IdMapper, serialize, name-munging, sum/mean overloads

Modified Paths:
--------------
    scala-commons/trunk/src/commons/Collections.scala

Modified: scala-commons/trunk/src/commons/Collections.scala
===================================================================
--- scala-commons/trunk/src/commons/Collections.scala	2008-02-15 02:30:16 UTC (rev 429)
+++ scala-commons/trunk/src/commons/Collections.scala	2008-02-15 02:31:34 UTC (rev 430)
@@ -123,7 +123,9 @@
 
   def sum(xs: Iterator[Int]) = xs.foldLeft(0)(_+_)
   def sum(xs: Seq[Double]) = xs reduceLeft ((x:Double,y:Double)=>x+y)
+  def sum(xs: Iterator[Double]) = xs reduceLeft ((_:Double)+(_:Double))
   def mean(xs: Seq[Int]) = sum(xs.elements) / xs.size
+  def mean(xs: Seq[Double]) = sum(xs.elements) / xs.size
   def median(xs: Seq[Long]) = xs(xs.length / 2)
 
   /**
@@ -657,7 +659,10 @@
   }
   def camelToUnder(s: String) = camelToLower(s, "_")
   def camelToHyphen(s: String) = camelToLower(s, "-")
+  def camelToSpaced(s: String) = camelToLower(s, " ")
 
+  def spacedToHyphen(s: String) = s replaceAll (" ", "-")
+
   // TODO: this isn't really rot encoding
   def rot(n: Int, s: String) = s map (_ + n toChar) mkString
 
@@ -693,4 +698,79 @@
       case Seq(a, b, rest @ _*) => Stream cons ((a,b), pairs(rest))
     }
   }
+
+  /**
+   * Maps unique IDs to distinct objects.
+   */
+  class IdMapper[a] extends mut.HashMap[a,Int] {
+    val i = Iterator from 0
+    override def default(k: a) = {
+      val n = i.next
+      this(k) = n
+      n
+    }
+  }
+
+  /**
+   * Serialize an Int to a String of four bytes (little-endian).
+   */
+  def serializeInt(i: Int) =
+    Array(
+      (i >>>  0) & 0xff,
+      (i >>>  8) & 0xff,
+      (i >>> 16) & 0xff,
+      (i >>> 24) & 0xff
+    ).map(_.toChar).mkString
+
+  /**
+   * For each x in xs, if p(x), then x is a header, and it owns all the xs
+   * after it until the next x for which p(x) holds. The return value is the
+   * header and its body.
+   * <p>
+   * <code>
+   * groupByHeaders([1,2,3,4,5,6,7,8,9])(_%3==0) == [[3,4,5],[6,7,8],[9]]
+   * </code>
+   */
+  def groupByHeaders[a](xs: Seq[a])(p: a => Boolean) = {
+    val ys = new mut.ArrayBuffer[mut.ArrayBuffer[a]]
+    for (x <- xs) {
+      if (p(x)) ys += new mut.ArrayBuffer[a]
+      if (!ys.isEmpty) ys.last += x
+    }
+    ys
+  }
+//  def groupByHeaders[a](xs: Seq[a])(p: a => Boolean) = {
+//    def r(seq: Seq[a]): Stream[List[a]] = seq match {
+//      case Seq()        => Stream.empty
+//      case Seq(y,ys@_*) => {
+//        val (as,bs) = spanBy(ys)(not(p))
+//        Stream.cons(y :: as.toList, r(bs))
+//      }
+//    }
+//    r(xs dropWhile (not(p)))
+//  }
+
+  /**
+   * <code>
+   * separateHeads([[a,b,c],[d,e,f,g],[],[h]])
+   *   == [(a,[b,c]),(d,[e,f,g]),(h,[])]
+   * </code>
+   */
+  def separateHeads[a](xss: Seq[Seq[a]]) =
+    for (xs <- xss; (Seq(a),b) = span(1)(xs)) yield (a,b)
+
+
+  /**
+   * Construct a multimap out of the given key-value pairs; the result maps
+   * keys to sets of values.
+   */
+  def multimap[a,b](xs: Iterable[(a,b)]) = {
+    val h = new mut.HashMap[a,mut.Set[b]] with mut.MultiMap[a,b] {
+      override def makeSet = new mut.HashSet[b]
+    }
+    for ((k,v) <- xs) {
+      h add (k,v)
+    }
+    h
+  }
 }


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