feat: Add row object iterator support.

src/table/column-table.js

@@ -10,7 +10,7 @@ import toMarkdown from '../format/to-markdown';
 import arrayType from '../util/array-type';
 import error from '../util/error';
 import mapObject from '../util/map-object';
-import unroll from '../util/unroll';
+import rowObjectBuilder from '../util/row-object-builder';
 
 /**
  * Class representing a table backed by a named set of columns.
@@ -113,14 +113,8 @@ export default class ColumnTable extends Table {
   objects(options = {}) {
     const limit = numRows(this, options.limit);
     if (limit <= 0) return [];
-
     const tuples = Array(limit);
-    const names = this.columnNames();
-    const create = unroll(
-      names.map(name => this.column(name)),
-      'row',
-      '({' + names.map((_, i) => `${JSON.stringify(_)}:_${i}.get(row)`) + '})'
-    );
+    const create = rowObjectBuilder(this);
 
     let r = 0;
     this.scan((row, data, stop) => {
@@ -131,6 +125,26 @@ export default class ColumnTable extends Table {
     return tuples;
   }
 
+  /**
+   * Returns an iterator over objects representing table rows.
+   * @return {Iterator} An iterator over row objects.
+   */
+  *[Symbol.iterator]() {
+    const create = rowObjectBuilder(this);
+    const n = this.numRows();
+
+    if (this.isOrdered() || this.isFiltered) {
+      const indices = this.indices();
+      for (let i = 0; i < n; ++i) {
+        yield create(indices[i]);
+      }
+    } else {
+      for (let i = 0; i < n; ++i) {
+        yield create(i);
+      }
+    }
+  }
+
   /**
    * Create a new fully-materialized instance of this table.
    * All filter and orderby settings are removed from the new table.

src/table/table.js

@@ -229,6 +229,14 @@ export default class Table {
     error('Not implemented');
   }
 
+  /**
+   * Returns an iterator over objects representing table rows.
+   * @return {Iterator} An iterator over row objects.
+   */
+  [Symbol.iterator]() {
+    error('Not implemented');
+  }
+
   /**
    * Print the contents of this table using the console.table() method.
    * @param {ObjectsOptions} options The options for row object generation,
@@ -350,7 +358,7 @@ export default class Table {
     const stop = () => i = this._total;
 
     if (order && this.isOrdered() || filter && this._index) {
-      const index = this._index = this.indices();
+      const index = this.indices();
       const data = this._data;
       for (; i < nrows; ++i) {
         fn(index[i], data, stop);

src/util/row-object-builder.js

@@ -0,0 +1,10 @@
+import unroll from './unroll';
+
+export default function(table, names) {
+  names = names || table.columnNames();
+  return unroll(
+    names.map(name => table.column(name)),
+    'row',
+    '({' + names.map((_, i) => `${JSON.stringify(_)}:_${i}.get(row)`) + '})'
+  );
+}

test/table/column-table-test.js

@@ -117,6 +117,30 @@ tape('ColumnTable supports object output', t => {
   t.end();
 });
 
+tape('ColumnTable supports iterator output', t => {
+  const output = [
+    { u: 'a', v: 2 },
+    { u: 'a', v: 1 },
+    { u: 'a', v: 4 },
+    { u: 'b', v: 5 },
+    { u: 'b', v: 3 }
+  ];
+
+  const dt = new ColumnTable({
+      u: ['a', 'a', 'a', 'b', 'b'],
+      v: [2, 1, 4, 5, 3]
+    });
+
+  t.deepEqual([...dt], output, 'iterator data');
+  t.deepEqual(
+    [...dt.orderby('v')],
+    output.slice().sort((a, b) => a.v - b.v),
+    'iterator data orderby'
+  );
+
+  t.end();
+});
+
 tape('ColumnTable toString shows table state', t => {
   const dt = new ColumnTable({
     a: ['a', 'a', 'a', 'b', 'b'],