diff --git a/modules/seq/alg/doc/seqalg.rst b/modules/seq/alg/doc/seqalg.rst
index 02f74c4f78015926f5faae38c54d5a4c72f24218..b846283f30ff5b7a2ec7d319cf91b7c65195d4cb 100644
--- a/modules/seq/alg/doc/seqalg.rst
+++ b/modules/seq/alg/doc/seqalg.rst
@@ -118,3 +118,18 @@
:param gap_open: The gap opening penalty. Must be a negative number
:param gap_ext: The gap extension penalty. Must be a negative number
:returns: best-scoring alignment of *seq1* and *seq2*.
+
+.. function:: ShannonEntropy(aln, ignore_gaps=True)
+
+ Returns the per-column Shannon entropies of the alignment. The entropy
+ describes how conserved a certain column in the alignment is . The higher
+ the entropy is, the less conserved the column. For column with no amino
+ aids, the entropy value is set to NAN
+
+ :param aln: multiple sequence alignment
+ :type aln: :class:`~ost.seq.AlignmentHandle`
+ :param ignore_gaps: whether to ignore gaps in the column.
+ :type ignore_gaps: bool
+
+ :returns: list of column entropies
+
diff --git a/modules/seq/alg/pymod/wrap_seq_alg.cc b/modules/seq/alg/pymod/wrap_seq_alg.cc
index 9239d1ec3d2e759729cfb1bcde0fb9005e52ded1..f22866761d38ac9c19fbe44b7f6d97cc41c27827 100644
--- a/modules/seq/alg/pymod/wrap_seq_alg.cc
+++ b/modules/seq/alg/pymod/wrap_seq_alg.cc
@@ -26,6 +26,7 @@
#include <ost/seq/alg/subst_weight_matrix.hh>
#include <ost/seq/alg/local_align.hh>
#include <ost/seq/alg/global_align.hh>
+#include <ost/seq/alg/entropy.hh>
using namespace boost::python;
using namespace ost::seq;
using namespace ost::seq::alg;
@@ -58,5 +59,6 @@ BOOST_PYTHON_MODULE(_ost_seq_alg)
arg("gap_open")=-5, arg("gap_ext")=-2));
def("GlobalAlign", &GlobalAlign,(arg("seq1"),arg("seq2"),arg("subst_weight"),
arg("gap_open")=-5, arg("gap_ext")=-2));
+ def("ShannonEntropy", &ShannonEntropy, (arg("aln"), arg("ignore_gaps")=true));
}
diff --git a/modules/seq/alg/src/CMakeLists.txt b/modules/seq/alg/src/CMakeLists.txt
index ccffcacf464cc22d85f62a6d5190067b76622cb7..ea6284a98d46e553879c2f7266e8d6d27289e19b 100644
--- a/modules/seq/alg/src/CMakeLists.txt
+++ b/modules/seq/alg/src/CMakeLists.txt
@@ -4,6 +4,7 @@ module_config.hh
ins_del.hh
subst_weight_matrix.hh
alignment_opts.hh
+entropy.hh
merge_pairwise_alignments.hh
conservation.hh
local_align.hh
@@ -14,6 +15,7 @@ set(OST_SEQ_ALG_SOURCES
merge_pairwise_alignments.cc
local_align.cc
global_align.cc
+entropy.cc
sequence_identity.cc
ins_del.cc
conservation.cc
diff --git a/modules/seq/alg/src/entropy.cc b/modules/seq/alg/src/entropy.cc
new file mode 100644
index 0000000000000000000000000000000000000000..7881512578187af9a0439ffe1ef44d5bab46dfe9
--- /dev/null
+++ b/modules/seq/alg/src/entropy.cc
@@ -0,0 +1,68 @@
+//------------------------------------------------------------------------------
+// This file is part of the OpenStructure project <www.openstructure.org>
+//
+// Copyright (C) 2008-2011 by the OpenStructure authors
+//
+// This library is free software; you can redistribute it and/or modify it under
+// the terms of the GNU Lesser General Public License as published by the Free
+// Software Foundation; either version 3.0 of the License, or (at your option)
+// any later version.
+// This library is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+// details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this library; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+//------------------------------------------------------------------------------
+#include <limits>
+
+#include "entropy.hh"
+
+#include <ost/seq/aligned_column.hh>
+#include <ost/seq/aligned_column_iterator.hh>
+
+namespace ost { namespace seq { namespace alg {
+
+int OneLetterCodeToIndex(char olc, bool ignore_gaps)
+{
+ if (olc >= 'A' && olc <= 'Z') return (olc-'A');
+ if (olc >= 'a' && olc <= 'z') return (olc-'a');
+ if (olc == '-' && !ignore_gaps) return 26;
+ return -1;
+}
+
+std::vector<Real> ShannonEntropy(const AlignmentHandle& aln, bool ignore_gaps) {
+ std::vector<Real> entropies(aln.GetLength(), 0);
+ int aa_counts[27];
+ int k = 0;
+ for (AlignmentHandle::iterator
+ i = aln.begin(), e = aln.end(); i != e; ++i, ++k) {
+ const AlignedColumn& col = *i;
+ memset(aa_counts, 0, sizeof(int)*27);
+ int counts = 0;
+ for (int j=0; j<aln.GetCount(); ++j) {
+ int index = OneLetterCodeToIndex(col[j], ignore_gaps);
+ if (index==-1) {
+ continue;
+ }
+ counts += 1;
+ aa_counts[index] += 1;
+ }
+ Real entropy = 0.0;
+ for (int j = 0; j < 27; ++j) {
+ if (aa_counts[j]) {
+ Real freq = static_cast<Real>(aa_counts[j])/counts;
+ entropy-= log(freq)*freq;
+ }
+ }
+ if (counts)
+ entropies[k] = entropy;
+ else
+ entropies[k] = std::numeric_limits<Real>::quiet_NaN();
+ }
+ return entropies;
+}
+
+}}}
diff --git a/modules/seq/alg/src/entropy.hh b/modules/seq/alg/src/entropy.hh
new file mode 100644
index 0000000000000000000000000000000000000000..85ec4ac0d6a9ab60cda514d64e4e277f6d6f80a9
--- /dev/null
+++ b/modules/seq/alg/src/entropy.hh
@@ -0,0 +1,36 @@
+//------------------------------------------------------------------------------
+// This file is part of the OpenStructure project <www.openstructure.org>
+//
+// Copyright (C) 2008-2011 by the OpenStructure authors
+//
+// This library is free software; you can redistribute it and/or modify it under
+// the terms of the GNU Lesser General Public License as published by the Free
+// Software Foundation; either version 3.0 of the License, or (at your option)
+// any later version.
+// This library is distributed in the hope that it will be useful, but WITHOUT
+// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+// FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
+// details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with this library; if not, write to the Free Software Foundation, Inc.,
+// 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+//------------------------------------------------------------------------------
+#ifndef OST_SEQ_ALG_ENTROPY_HH
+#define OST_SEQ_ALG_ENTROPY_HH
+
+#include <vector>
+
+#include <ost/seq/alignment_handle.hh>
+
+#include "module_config.hh"
+
+namespace ost { namespace seq { namespace alg {
+
+/// \brief calculates the Shannon entropy for each column in the alignment
+std::vector<Real> DLLEXPORT_OST_SEQ_ALG ShannonEntropy(const AlignmentHandle& aln,
+ bool ignore_gaps=true);
+
+}}}
+#endif
+