From 9fe9437445ba7f93374354f48a641f4ba6d847b4 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Sun, 9 Sep 2012 11:38:59 -0700
Subject: [PATCH] math.transforms.bwt: adding inefficient versions of
 Burrows-Wheeler transform.

---
 extra/math/transforms/bwt/authors.txt      |  1 +
 extra/math/transforms/bwt/bwt-tests.factor |  6 ++++++
 extra/math/transforms/bwt/bwt.factor       | 15 +++++++++++++++
 extra/math/transforms/bwt/summary.txt      |  1 +
 4 files changed, 23 insertions(+)
 create mode 100644 extra/math/transforms/bwt/authors.txt
 create mode 100644 extra/math/transforms/bwt/bwt-tests.factor
 create mode 100644 extra/math/transforms/bwt/bwt.factor
 create mode 100644 extra/math/transforms/bwt/summary.txt

diff --git a/extra/math/transforms/bwt/authors.txt b/extra/math/transforms/bwt/authors.txt
new file mode 100644
index 0000000000..e091bb8164
--- /dev/null
+++ b/extra/math/transforms/bwt/authors.txt
@@ -0,0 +1 @@
+John Benediktsson
diff --git a/extra/math/transforms/bwt/bwt-tests.factor b/extra/math/transforms/bwt/bwt-tests.factor
new file mode 100644
index 0000000000..a5b9856bca
--- /dev/null
+++ b/extra/math/transforms/bwt/bwt-tests.factor
@@ -0,0 +1,6 @@
+! Copyright (C) 2012 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: strings tools.test ;
+IN: math.transforms.bwt
+
+{ "asdf" } [ "asdf" bwt ibwt >string ] unit-test
diff --git a/extra/math/transforms/bwt/bwt.factor b/extra/math/transforms/bwt/bwt.factor
new file mode 100644
index 0000000000..4415c5136c
--- /dev/null
+++ b/extra/math/transforms/bwt/bwt.factor
@@ -0,0 +1,15 @@
+! Copyright (C) 2012 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+USING: arrays fry kernel math sequences sequences.extras
+sorting ;
+IN: math.transforms.bwt
+
+! Inefficient versions of Burrows-Wheeler Transform
+
+: bwt ( seq -- newseq )
+    { 0 } swap append all-rotations natural-sort [ last ] map ;
+
+: ibwt ( newseq -- seq )
+    [ length [ { } <array> ] keep ] keep
+    '[ _ [ prefix ] 2map natural-sort ] times
+    [ { 0 } tail? ] find nip 1 head* ;
diff --git a/extra/math/transforms/bwt/summary.txt b/extra/math/transforms/bwt/summary.txt
new file mode 100644
index 0000000000..2445877b41
--- /dev/null
+++ b/extra/math/transforms/bwt/summary.txt
@@ -0,0 +1 @@
+Burrows-Wheeler Transform