Added seq-utils.clj: sequence utilities.

1 files changed, 50 insertions, 0 deletions

diff --git a/seq-utils.clj b/seq-utils.clj
new file mode 100644
index 00000000..eafceebc
--- /dev/null
+++ b/seq-utils.clj
@@ -0,0 +1,50 @@
+;;; seq-utils.clj -- Sequence utilities for Clojure
+
+;; by Stuart Sierra <mail@stuartsierra.com>
+;; April 8, 2008
+
+;; Copyright (c) 2008 Stuart Sierra. All rights reserved.  The use and
+;; distribution terms for this software are covered by the Common
+;; Public License 1.0 (http://www.opensource.org/licenses/cpl1.0.php)
+;; which can be found in the file CPL.TXT at the root of this
+;; distribution.  By using this software in any fashion, you are
+;; agreeing to be bound by the terms of this license.  You must not
+;; remove this notice, or any other, from this software.
+
+
+(clojure/in-ns 'seq-utils)
+(clojure/refer 'clojure)
+
+
+;; 'flatten' written by Rich Hickey,
+;; see http://groups.google.com/group/clojure/msg/385098fabfcaad9b
+(defn flatten
+  "Takes any nested combination of sequential things (lists, vectors,
+  etc.) and returns their contents as a single, flat sequence."
+  [x]
+  (let [s? #(instance? clojure.lang.Sequential %)]
+    (filter (complement s?) (tree-seq s? seq x))))
+
+(defn batch
+  "Divides 'coll' into sequences each containing 'size' elements,
+  returns a sequence of those sequences.  The last sequence may
+  have fewer than 'size' elements."
+  [size coll]
+  (when coll
+    (lazy-cons (take size coll) (batch size (drop size coll)))))
+
+(defn separate
+  "Separates elements in 'coll' into two sequences, one for which 
+  (f item) is logical true, the other for which (f item) is logical
+  false.  Returns a vector containing two (lazy) sequences:
+     [ (true-items) (false-items) ]"
+  [f coll]
+  [(filter f coll) (filter (complement f) coll)])
+
+(defn includes?
+  "Returns true if 'coll' (a sequential collection) contains 'value',
+  false otherwise.  Uses '=' to test equality.  May scan the entire
+  collection."
+  [value coll]
+  (if (some (fn [x] (= x value)) coll)
+    true false))