Fleshed out example program.

python_examples/sequence_segmenter.py

@@ -2,75 +2,104 @@
 # The contents of this file are in the public domain. See LICENSE_FOR_EXAMPLE_PROGRAMS.txt
 #
 # 
-# You need to compile the dlib python interface before you can use this
-# file.  To do this, run compile_dlib_python_module.bat.  You also need to
-# have the boost-python library installed.  On Ubuntu, this can be done easily by running
-# the command: sudo apt-get install libboost-python-dev
+# This example program shows how to use the dlib sequence segmentation tools from within a
+# python program.  In particular, we will create a simple training dataset, learn a
+# sequence segmentation model, and then test it on some sequences.  
+#
+# COMPILING THE DLIB PYTHON INTERFACE
+#   You need to compile the dlib python interface before you can use this file.  To do
+#   this, run compile_dlib_python_module.bat.  This should work on any operating system so
+#   long as you have CMake and boost-python installed.  On Ubuntu, this can be done easily
+#   by running the command: sudo apt-get install libboost-python-dev cmake
 
-#  asfd
-import dlib
 
-use_sparse_vects = False 
+import dlib
 
-if use_sparse_vects:
-    samples = dlib.sparse_vectorss()
-else:
-    samples = dlib.vectorss()
 
-segments = dlib.rangess()
+# In a sequence segmentation task we are given a sequence of objects (e.g. words in a
+# sentence) and we are supposed to detect certain subsequences (e.g. named entities).  In
+# the code below we create some very simple sequence/segmentation training pairs.  In
+# particular, each element of a sequence is represented by a vector which describes
+# important properties of the element.  The idea is to use vectors that contain information
+# useful for detecting whatever kind of subsequences you are interested in detecting.  
 
+# To keep this example simple we will use very simple vectors.  Specifically, each vector
+# is 2D and is either the vector [0 1] or [1 0].  Moreover, we will say that the
+# subsequences we want to detect are any runs of the [0 1] vector.  Note that the code
+# works with both dense and sparse vectors.  The following if statement constructs either
+# kind depending on the value in use_sparse_vects.
+use_sparse_vects = False 
 if use_sparse_vects:
+    training_sequences = dlib.sparse_vectorss()
     inside = dlib.sparse_vector()
     outside = dlib.sparse_vector()
+    # Add index/value pairs to each sparse vector.  Any index not mentioned in a sparse
+    # vector is implicitly associated with a value of zero.
     inside.append(dlib.pair(0,1))
     outside.append(dlib.pair(1,1))
 else:
+    training_sequences = dlib.vectorss()
     inside = dlib.vector([0, 1])
     outside = dlib.vector([1, 0])
 
-samples.resize(2)
+# Here we make our training sequences and their annotated subsegments.  We create two
+# training sequences. 
+segments = dlib.rangess()
+training_sequences.resize(2)
 segments.resize(2)
 
-samples[0].append(outside)
-samples[0].append(outside)
-samples[0].append(inside)
-samples[0].append(inside)
-samples[0].append(inside)
-samples[0].append(outside)
-samples[0].append(outside)
-samples[0].append(outside)
+# training_sequences[0] starts out empty and we append vectors onto it.  Note that we wish
+# to detect the subsequence of "inside" vectors within the sequence.  So the output should
+# be the range (2,5).  Note that this is a "half open" range meaning that it starts with
+# the element with index 2 and ends just before the element with index 5.
+training_sequences[0].append(outside) # index 0
+training_sequences[0].append(outside) # index 1
+training_sequences[0].append(inside)  # index 2
+training_sequences[0].append(inside)  # index 3
+training_sequences[0].append(inside)  # index 4
+training_sequences[0].append(outside) # index 5
+training_sequences[0].append(outside) # index 6
+training_sequences[0].append(outside) # index 7
 segments[0].append(dlib.range(2,5))
 
-
-samples[1].append(outside)
-samples[1].append(outside)
-samples[1].append(inside)
-samples[1].append(inside)
-samples[1].append(inside)
-samples[1].append(inside)
-samples[1].append(outside)
-samples[1].append(outside)
+# Add another training sequence
+training_sequences[1].append(outside) # index 0
+training_sequences[1].append(outside) # index 1
+training_sequences[1].append(inside)  # index 2
+training_sequences[1].append(inside)  # index 3
+training_sequences[1].append(inside)  # index 4
+training_sequences[1].append(inside)  # index 5
+training_sequences[1].append(outside) # index 6
+training_sequences[1].append(outside) # index 7
 segments[1].append(dlib.range(2,6))
 
 
+# Now that we have a simple training set we can train a sequence segmenter.  However, the
+# sequence segmentation trainer has some optional parameters we can set.  These parameters
+# determine properties of the segmentation model we will learn.  See the dlib documentation
+# for the sequence_segmenter object for a full discussion of their meanings.
 params = dlib.segmenter_params()
-#params.be_verbose = True
 params.window_size = 1
 params.use_high_order_features = False
-params.C = 1
-print "params:", params
-
-df = dlib.train_sequence_segmenter(samples, segments, params)
-
-print len(df.segment_sequence(samples[0]))
-print df.segment_sequence(samples[0])[0]
+params.use_BIO_model = True
+params.C = 1 
 
+# Train a model
+model = dlib.train_sequence_segmenter(training_sequences, segments, params)
 
+# A segmenter model takes a sequence of vectors and returns an array of detected ranges.
+# So for example, we can give it the first training sequence and it will predict the
+# locations of the subsequences.  This statement will correctly print 2,5.
+print model.segment_sequence(training_sequences[0])[0]
 
-print df.weights
+# We can also measure the accuracy of a model relative to some labeled data.  This
+# statement prints the precision, recall, and F1-score of the model relative to the data in
+# training_sequences/segments.
+print "Test on training data:", dlib.test_sequence_segmenter(model, training_sequences, segments)
 
-#res = dlib.test_sequence_segmenter(df, samples, segments)
-res = dlib.cross_validate_sequence_segmenter(samples, segments, 2, params)
+# We can also do n-fold cross-validation and print the resulting precision, recall, and
+# F1-score.
+num_folds = 2
+print "cross validation:", dlib.cross_validate_sequence_segmenter(training_sequences, segments, num_folds, params)
 
-print res