feat(*): enhance its/as helpers for vectorizer

Author: sanjayaksaxena

src/as.js

@@ -30,6 +30,7 @@
 
 //
 
+var sort4FT = require( './sort4FT.js' );
 var containedMarkings = require( './contained-markings.js' );
 var as = Object.create( null );
 
@@ -88,7 +89,7 @@ as.freqTable = function ( tokens ) {
     table[ i ] = [ keys[ i ], bow[ keys[ i ] ] ];
   }
 
-  return table.sort( ( a, b ) => ( b[ 1 ] - a[ 1 ] ) );
+  return table.sort( sort4FT );
 }; // freqTable()
 
 // ### bigrams

src/its.js

@@ -30,6 +30,7 @@
 
 //
 
+var sort4FT = require( './sort4FT.js' );
 var constants = require( './constants.js' );
 var caseMap = [ 'other', 'lowerCase', 'upperCase', 'titleCase' ];
 
@@ -138,5 +139,51 @@ its.sentiment = function ( spanItem ) {
   return spanItem[ 3 ];
 }; // span()
 
+/* ------ utilities ------ */
+
+its.terms = function ( tf, idf, terms ) {
+  return terms;
+}; // terms()
+
+its.docTermMatrix = function ( tf, idf, terms ) {
+  const dtm = new Array( tf.length );
+  for ( let id = 0; id < tf.length; id += 1 ) {
+    dtm[ id ] = [];
+    for ( let i = 0; i < terms.length; i += 1 ) {
+      dtm[ id ].push( tf[ id ][ terms[ i ] ] || 0 );
+    }
+  }
+  return dtm;
+}; // getDocTermMatrix()
+
+its.docBOWArray = function ( tf ) {
+  return tf;
+}; // docBOWArray()
+
+its.bow = function ( tf ) {
+  return tf;
+}; // bow()
+
+its.idf = function ( tf, idf ) {
+  var arr = [];
+  for ( const t in idf ) { // eslint-disable-line guard-for-in
+    arr.push( [ t, idf[ t ] ] );
+  }
+  // Sort on frequency followed by the term.
+  return arr.sort( sort4FT );
+}; // idf()
+
+its.tf = function ( tf ) {
+  const arr = [];
+  for ( const t in tf ) {  // eslint-disable-line guard-for-in
+    arr.push( [ t, tf[ t ] ] );
+  }
+  // Sort on frequency followed by the term.
+  return arr.sort( sort4FT );
+}; // tf()
+
+its.modelJSON = function ( tf, idf ) {
+  return JSON.stringify( { tf: tf, idf: idf } );
+}; // model()
 
 module.exports = its;

src/sort4FT.js

@@ -0,0 +1,16 @@
+/**
+ * Stable sort function for frequency table i.e. `[ [ term, frequency ] ... ]`.
+ * It first sorts on the frequency and then an alpha-numeric sort on term.
+ *
+ * @param  {array}  a first term-frequency pair element sent by sort.
+ * @param  {array}  b second term-frequency pair element sent by sort.
+ * @return {number}   number: -1 or 0 or +1.
+ */
+module.exports = ( a, b ) => {
+  if ( b[ 1 ] > a[ 1 ] ) {
+    return 1;
+  } else if ( b[ 1 ] < a[ 1 ] ) {
+           return -1;
+         } else if ( a[ 0 ] > b[ 0 ] ) return 1;
+  return -1;
+};