Added example for bag groupby and foldby as requested in issue 46

Author: enstenr

bag.ipynb

@@ -138,6 +138,25 @@
     "b.count().compute()  # Count total number of records"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "(b.groupby(lambda record:record[\"occupation\"]).map(lambda kv: ( kv[0], len(kv[1]))).compute()[:10]) # using groupby to count people in each occupation"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "city_counts = b.foldby(key = lambda record:record[\"address\"][\"city\"], binop = lambda acc, record:acc + 1, initial = 0 ) # using foldby to count people living by city\n",
+    "city_counts.take(10)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},