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;;; seq_utils.clj -- Sequence utilities for Clojure
;; by Stuart Sierra, http://stuartsierra.com/
;; last updated August 12, 2008
;; Copyright (c) Stuart Sierra, 2008. All rights reserved. The use
;; and distribution terms for this software are covered by the Eclipse
;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
;; which can be found in the file epl-v10.html 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.
(ns clojure.contrib.seq-utils)
;; '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 separate
"Returns a vector:
[ (filter f s), (filter (complement f) s) ]"
[f s]
[(filter f s) (filter (complement f) s)])
(defn includes?
"Returns true if s contains something equal (with =) to x."
[x s]
(if (some (fn [y] (= y x)) s)
true false))
(defn indexed
"Returns a lazy sequence of [index, item] pairs, where items come
from 's' and indexes count up from zero.
(indexed '(a b c d)) => ([0 a] [1 b] [2 c] [3 d])"
[s]
(map vector (iterate inc 0) s))
;; group-by written by Rich Hickey;
;; see http://paste.lisp.org/display/64190
(defn group-by
"Returns a sorted map of the elements of coll keyed by the result of
f on each element. The value at each key will be a vector of the
corresponding elements, in the order they appeared in coll."
[f coll]
(reduce
(fn [ret x]
(let [k (f x)]
(assoc ret k (conj (get ret k []) x))))
(sorted-map) coll))
;; partition-by written by Rich Hickey;
;; see http://paste.lisp.org/display/64190
(defn partition-by
"Applies f to each value in coll, splitting it each time f returns
a new value. Returns a lazy seq of lazy seqs."
[f coll]
(when-let [s (seq coll)]
(let [fv (f (first s))
ends (drop-while #(= fv (f %)) (rest s))
tw (fn this [s]
(when-not (identical? s ends)
(lazy-cons (first s) (this (rest s)))))]
(lazy-cons (tw s) (partition-by f ends)))))
(defn frequencies
"Returns a map from distinct items in coll to the number of times
they appear."
[coll]
(reduce (fn [counts x]
(assoc counts x (inc (get counts x 0))))
{} coll))
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