Add ngrams

First git commit from new laptop!

README.md

@@ -8,31 +8,34 @@ GPTC provides both a CLI tool and a Python library.
 
 ### Classifying text
 
-    python -m gptc classify <compiled model file>
+    python -m gptc classify [-n <max_ngram_length>] <compiled model file>
 
 This will prompt for a string and classify it, then print (in JSON) a dict of
-the format `{category: probability, category:probability, ...}` to stdout.
+the format `{category: probability, category:probability, ...}` to stdout. (For
+information about `-n <max_ngram_length>`, see section "Ngrams.")
 
 Alternatively, if you only need the most likely category, you can use this:
 
-    python -m gptc classify [-c|--category] <compiled model file>
+    python -m gptc classify [-n <max_ngram_length>] <-c|--category> <compiled model file>
 
 This will prompt for a string and classify it, outputting the category on
 stdout (or "None" if it cannot determine anything).
 
 ### Compiling models
 
-    python -m gptc compile <raw model file>
+    python -m gptc compile [-n <max_ngram_length>] <raw model file>
 
 This will print the compiled model in JSON to stdout.
 
 ## Library
 
-### `gptc.Classifier(model)`
+### `gptc.Classifier(model, max_ngram_length=1)`
 
 Create a `Classifier` object using the given *compiled* model (as a dict, not
 JSON).
 
+For information about `max_ngram_length`, see section "Ngrams."
+
 #### `Classifier.confidence(text)`
 
 Classify `text`. Returns a dict of the format `{category: probability,
@@ -43,10 +46,32 @@ category:probability, ...}`
 Classify `text`. Returns the category into which the text is placed (as a
 string), or `None` when it cannot classify the text.
 
-### `gptc.compile(raw_model)`
+### `gptc.compile(raw_model, max_ngram_length=1)`
 Compile a raw model (as a list, not JSON) and return the compiled model (as a
 dict).
 
+For information about `max_ngram_length`, see section "Ngrams."
+
+## Ngrams
+
+GPTC optionally supports using ngrams to improve classification accuracy. They
+are disabled by default (maximum length set to 1) for performance and
+compatibility reasons. Enabling them significantly increases the time required
+both for compilation and classification. The effect seems more significant for
+compilation than for classification. Compiled models are also much larger when
+ngrams are enabled. Larger maximum ngram lengths will result in slower
+performance and larger files. It is a good idea to experiment with different
+values and use the highest one at which GPTC is fast enough and models are
+small enough for your needs.
+
+Once a model is compiled at a certain maximum ngram length, it cannot be used
+for classification with a higher value. If you instantiate a `Classifier` with
+a model compiled with a lower `max_ngram_length`, the value will be silently
+reduced to the one used when compiling the model.
+
+Models compiled with older versions of GPTC which did not support ngrams are
+handled the same way as models compiled with `max_ngram_length=1`.
+
 ## Model format
 
 This section explains the raw model format, which is how you should create and
@@ -73,6 +98,8 @@ Mark Twain and those written by William Shakespeare, is available in `models`.
 The raw model is in `models/raw.json`; the compiled model is in
 `models/compiled.json`.
 
+The example model was compiled with `max_ngram_length=10`.
+
 ## Benchmark
 
 A benchmark script is available for comparing performance of GPTC between

benchmark.py

@@ -3,6 +3,7 @@ import gptc
 import json
 import sys
 
+max_ngram_length = 10
 compile_iterations = 100
 classify_iterations = 10000
 
@@ -12,9 +13,8 @@ with open("models/raw.json") as f:
 with open("models/benchmark_text.txt") as f:
     text = f.read()
 
-classifier = gptc.Classifier(gptc.compile(raw_model))
-
 print("Benchmarking GPTC on Python", sys.version)
+print("Maximum ngram length:", max_ngram_length)
 
 print(
     "Average compilation time over",
@@ -23,7 +23,7 @@ print(
     round(
         1000000
         * timeit.timeit(
-            "gptc.compile(raw_model)",
+            "gptc.compile(raw_model, max_ngram_length)",
             number=compile_iterations,
             globals=globals(),
         )
@@ -33,6 +33,7 @@ print(
 )
 
 
+classifier = gptc.Classifier(gptc.compile(raw_model, max_ngram_length), max_ngram_length)
 print(
     "Average classification time over",
     classify_iterations,
@@ -48,3 +49,4 @@ print(
     ),
     "microseconds",
 )
+print("--- benchmark complete ---")

gptc/__main__.py

@@ -6,14 +6,18 @@ import json
 import sys
 import gptc
 
-parser = argparse.ArgumentParser(description="General Purpose Text Classifier", prog='gptc')
+parser = argparse.ArgumentParser(
+    description="General Purpose Text Classifier", prog="gptc"
+)
 subparsers = parser.add_subparsers(dest="subparser_name", required=True)
 
-compile_parser = subparsers.add_parser('compile', help='compile a raw model')
+compile_parser = subparsers.add_parser("compile", help="compile a raw model")
 compile_parser.add_argument("model", help="raw model to compile")
+compile_parser.add_argument("--max-ngram-length", "-n", help="maximum ngram length", type=int, default=1)
 
-classify_parser = subparsers.add_parser('classify', help='classify text')
+classify_parser = subparsers.add_parser("classify", help="classify text")
 classify_parser.add_argument("model", help="compiled model to use")
+classify_parser.add_argument("--max-ngram-length", "-n", help="maximum ngram length", type=int, default=1)
 group = classify_parser.add_mutually_exclusive_group()
 group.add_argument(
     "-j",
@@ -33,10 +37,10 @@ args = parser.parse_args()
 with open(args.model, "r") as f:
     model = json.load(f)
 
-if args.subparser_name == 'compile':
-    print(json.dumps(gptc.compile(model)))
+if args.subparser_name == "compile":
+    print(json.dumps(gptc.compile(model, args.max_ngram_length)))
 else:
-    classifier = gptc.Classifier(model)
+    classifier = gptc.Classifier(model, args.max_ngram_length)
 
     if sys.stdin.isatty():
         text = input("Text to analyse: ")

gptc/classifier.py

@@ -12,6 +12,11 @@ class Classifier:
     model : dict
         A compiled GPTC model.
 
+    max_ngram_length : int
+        The maximum ngram length to use when tokenizing input. If this is
+        greater than the value used when the model was compiled, it will be
+        silently lowered to that value.
+
     Attributes
     ----------
     model : dict
@@ -19,12 +24,15 @@ class Classifier:
 
     """
 
-    def __init__(self, model):
+    def __init__(self, model, max_ngram_length=1):
         if model.get("__version__", 0) != 3:
             raise gptc.exceptions.UnsupportedModelError(
                 f"unsupported model version"
             )
         self.model = model
+        self.max_ngram_length = min(
+            max_ngram_length, model.get("__ngrams__", 1)
+        )
 
     def confidence(self, text):
         """Classify text with confidence.
@@ -44,7 +52,7 @@ class Classifier:
 
         model = self.model
 
-        text = gptc.tokenizer.tokenize(text)
+        text = gptc.tokenizer.tokenize(text, self.max_ngram_length)
         probs = {}
         for word in text:
             try:

gptc/compiler.py

@@ -3,7 +3,7 @@
 import gptc.tokenizer
 
 
-def compile(raw_model):
+def compile(raw_model, max_ngram_length=1):
     """Compile a raw model.
 
     Parameters
@@ -11,6 +11,9 @@ def compile(raw_model):
     raw_model : list of dict
         A raw GPTC model.
 
+    max_ngram_length : int
+        Maximum ngram lenght to compile with.
+
     Returns
     -------
     dict
@@ -21,7 +24,7 @@ def compile(raw_model):
     categories = {}
 
     for portion in raw_model:
-        text = gptc.tokenizer.tokenize(portion["text"])
+        text = gptc.tokenizer.tokenize(portion["text"], max_ngram_length)
         category = portion["category"]
         try:
             categories[category] += text
@@ -64,7 +67,7 @@ def compile(raw_model):
             )
 
     model["__names__"] = names
-
+    model["__ngrams__"] = max_ngram_length
     model["__version__"] = 3
 
     return model

gptc/tokenizer.py

@@ -1,14 +1,23 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 
 
-def tokenize(text):
+def tokenize(text, max_ngram_length=1):
     """Convert a string to a list of lemmas."""
-    out = [""]
+    tokens = [""]
 
     for char in text.lower():
         if char.isalpha() or char == "'":
-            out[-1] += char
-        elif out[-1] != "":
-            out.append("")
+            tokens[-1] += char
+        elif tokens[-1] != "":
+            tokens.append("")
 
-    return [string for string in out if string]
+    tokens = [string for string in tokens if string]
+
+    if max_ngram_length == 1:
+        return tokens
+    else:
+        ngrams = []
+        for ngram_length in range(1, max_ngram_length + 1):
+            for index in range(len(tokens) + 1 - ngram_length):
+                ngrams.append(" ".join(tokens[index : index + ngram_length]))
+        return ngrams