Add ngrams operation

src/core/config/Categories.json

@@ -336,6 +336,7 @@
             "Pseudo-Random Number Generator",
             "Sleep",
             "File Tree",
+            "N-gram"
             "Take nth bytes",
             "Drop nth bytes"
         ]

src/core/operations/Ngram.mjs

@@ -0,0 +1,60 @@
+/**
+ * @author benjcal [[email protected]]
+ * @copyright Crown Copyright 2024
+ * @license Apache-2.0
+ */
+
+import Operation from "../Operation.mjs";
+import {JOIN_DELIM_OPTIONS} from "../lib/Delim.mjs";
+
+/**
+ * ngram operation
+ */
+class Ngram extends Operation {
+
+    /**
+     * Ngram constructor
+     */
+    constructor() {
+        super();
+
+        this.name = "N-gram";
+        this.module = "Default";
+        this.description = "Extracts n-grams from the input text. N-grams are contiguous sequences of n characters from a given text sample.";
+        this.infoURL = "https://wikipedia.org/wiki/N-gram";
+        this.inputType = "string";
+        this.outputType = "string";
+        this.args = [
+            {
+                name: "N-gram size",
+                type: "number",
+                value: 3
+            },
+            {
+                "name": "Join delimiter",
+                "type": "editableOptionShort",
+                "value": JOIN_DELIM_OPTIONS
+            }
+        ];
+    }
+
+    /**
+     * @param {string} input
+     * @param {Object[]} args
+     * @returns {string}
+     */
+    run(input, args) {
+        const nGramSize = args[0],
+            joinDelim = args[1];
+
+        const ngrams = [];
+        for (let i = 0; i <= input.length - nGramSize; i++) {
+            ngrams.push(input.slice(i, i + nGramSize));
+        }
+
+        return ngrams.join(joinDelim);
+    }
+
+}
+
+export default Ngram;

tests/operations/index.mjs

@@ -114,6 +114,7 @@ import "./tests/MS.mjs";
 import "./tests/MultipleBombe.mjs";
 import "./tests/MurmurHash3.mjs";
 import "./tests/NetBIOS.mjs";
+import "./tests/Ngram.mjs";
 import "./tests/NormaliseUnicode.mjs";
 import "./tests/NTLM.mjs";
 import "./tests/OTP.mjs";

tests/operations/tests/Ngram.mjs

@@ -0,0 +1,34 @@
+/**
+ * Ngram tests.
+ *
+ * @author jg42526
+ *
+ * @copyright Crown Copyright 2017
+ * @license Apache-2.0
+ */
+import TestRegister from "../../lib/TestRegister.mjs";
+
+TestRegister.addTests([
+    {
+        name: "Ngram 3",
+        input: "hello",
+        expectedOutput: "hel,ell,llo",
+        recipeConfig: [
+            {
+                op: "N-gram",
+                args: ["3", ","],
+            },
+        ],
+    },
+    {
+        name: "Ngram longer than input",
+        input: "hello",
+        expectedOutput: "",
+        recipeConfig: [
+            {
+                op: "N-gram",
+                args: ["6", ","],
+            },
+        ],
+    },
+]);