[parser] Averaged perceptron tagger

src/averaged_perceptron_tagger.c

@@ -0,0 +1,44 @@
+#include "averaged_perceptron_tagger.h"
+
+
+
+bool averaged_perceptron_tagger_predict(averaged_perceptron_t *model, void *tagger, void *context, cstring_array *features, cstring_array *labels, ap_tagger_feature_function feature_function, tokenized_string_t *tokenized) {
+
+    // Keep two tags of history in training
+    char *prev = START;
+    char *prev2 = START2;
+
+    uint32_t prev_id = 0;
+    uint32_t prev2_id = 0;
+
+    size_t num_tokens = tokenized->tokens->n;
+
+    for (uint32_t i = 0; i < num_tokens; i++) {
+        cstring_array_clear(features);
+
+        if (i > 0) {
+            prev = cstring_array_get_string(labels, prev_id);
+        }
+
+        if (i > 1) {
+            prev2 = cstring_array_get_string(labels, prev2_id);            
+        }
+
+        if (!feature_function(tagger, context, tokenized, i, prev, prev2)) {
+            log_error("Could not add address parser features\n");
+            return false;
+        }
+
+        uint32_t guess = averaged_perceptron_predict(model, features);
+        char *predicted = cstring_array_get_string(model->classes, guess);
+
+        cstring_array_add_string(labels, predicted);
+
+        prev2_id = prev_id;
+        prev_id = guess;
+
+    }
+
+    return true;
+
+}

src/averaged_perceptron_tagger.h

@@ -0,0 +1,29 @@
+/*
+averaged_perceptron_tagger.h
+----------------------------
+
+An averaged perceptron tagger is a greedy sequence labeling
+algorithm which uses two tags of history.
+
+*/
+
+#ifndef AVERAGED_PERCEPTRON_TAGGER_H
+#define AVERAGED_PERCEPTRON_TAGGER_H
+
+#include <stdlib.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#include "averaged_perceptron.h"
+#include "tokens.h"
+
+#define START "START"
+#define START2 "START2"
+
+// Arguments:                              tagger, context, tokenized str, index, i-1 tag, i-2 tag
+typedef bool (*ap_tagger_feature_function)(void *, void *, tokenized_string_t *, uint32_t, char *, char *);
+
+bool averaged_perceptron_tagger_predict(averaged_perceptron_t *model, void *tagger, void *context, cstring_array *features, cstring_array *labels, ap_tagger_feature_function feature_function, tokenized_string_t *tokenized);
+
+#endif