Only flush column if not empty to avoid extraneous columnar_update ca…

…lls (#1538)

## Description

This doesn't have much effect on standard metrics, but we make an
extraneous call to columnar_update when converting to a view even if the
cache is empty, which leads to a surprising number of calls and updates
called with empty data.

## Changes

- Check if the cache if empty before flushing the cache in column
profiles

- [x] I have reviewed the [Guidelines for Contributing](CONTRIBUTING.md)
and the [Code of Conduct](CODE_OF_CONDUCT.md).

python/examples/advanced/Custom_Metrics.ipynb

@@ -173,7 +173,7 @@
     },
     {
       "cell_type": "code",
-      "execution_count": 4,
+      "execution_count": 3,
       "metadata": {
         "id": "HlFNH-H6-qKg"
       },
@@ -195,7 +195,7 @@
     },
     {
       "cell_type": "code",
-      "execution_count": 5,
+      "execution_count": 4,
       "metadata": {},
       "outputs": [
         {
@@ -219,16 +219,16 @@
               "  <thead>\n",
               "    <tr style=\"text-align: right;\">\n",
               "      <th></th>\n",
-              "      <th>histogram/n</th>\n",
               "      <th>histogram/max</th>\n",
+              "      <th>histogram/median</th>\n",
               "      <th>histogram/min</th>\n",
+              "      <th>histogram/n</th>\n",
               "      <th>histogram/q_10</th>\n",
               "      <th>histogram/q_25</th>\n",
-              "      <th>histogram/median</th>\n",
               "      <th>histogram/q_75</th>\n",
               "      <th>histogram/q_90</th>\n",
-              "      <th>struct/x</th>\n",
               "      <th>struct/s</th>\n",
+              "      <th>struct/x</th>\n",
               "      <th>type</th>\n",
               "    </tr>\n",
               "    <tr>\n",
@@ -249,37 +249,37 @@
               "  <tbody>\n",
               "    <tr>\n",
               "      <th>col1</th>\n",
-              "      <td>1</td>\n",
               "      <td>1.2</td>\n",
               "      <td>1.2</td>\n",
               "      <td>1.2</td>\n",
+              "      <td>1</td>\n",
               "      <td>1.2</td>\n",
               "      <td>1.2</td>\n",
               "      <td>1.2</td>\n",
               "      <td>1.2</td>\n",
-              "      <td>2</td>\n",
-              "      <td>aa</td>\n",
+              "      <td>a</td>\n",
+              "      <td>1</td>\n",
               "      <td>SummaryType.COLUMN</td>\n",
               "    </tr>\n",
               "  </tbody>\n",
               "</table>\n",
               "</div>"
             ],
             "text/plain": [
-              "        histogram/n  histogram/max  histogram/min  histogram/q_10  \\\n",
-              "column                                                              \n",
-              "col1              1            1.2            1.2             1.2   \n",
+              "        histogram/max  histogram/median  histogram/min  histogram/n  \\\n",
+              "column                                                                \n",
+              "col1              1.2               1.2            1.2            1   \n",
               "\n",
-              "        histogram/q_25  histogram/median  histogram/q_75  histogram/q_90  \\\n",
-              "column                                                                     \n",
-              "col1               1.2               1.2             1.2             1.2   \n",
+              "        histogram/q_10  histogram/q_25  histogram/q_75  histogram/q_90  \\\n",
+              "column                                                                   \n",
+              "col1               1.2             1.2             1.2             1.2   \n",
               "\n",
-              "        struct/x struct/s                type  \n",
+              "       struct/s  struct/x                type  \n",
               "column                                         \n",
-              "col1           2       aa  SummaryType.COLUMN  "
+              "col1          a         1  SummaryType.COLUMN  "
             ]
           },
-          "execution_count": 5,
+          "execution_count": 4,
           "metadata": {},
           "output_type": "execute_result"
         }
@@ -310,7 +310,7 @@
       "name": "python",
       "nbconvert_exporter": "python",
       "pygments_lexer": "ipython3",
-      "version": "3.8.10"
+      "version": "3.9.19"
     },
     "vscode": {
       "interpreter": {

python/whylogs/core/column_profile.py

@@ -47,7 +47,8 @@ def flush(self) -> None:
         logger.debug("Flushing out the cache for col: %s. Cache size: %s", self._name, self._cache_size)
         old_cache = self._cache
         self._cache = []
-        self.track_column(old_cache)
+        if old_cache:
+            self.track_column(old_cache)
 
     def _process_extracted_column(self, extracted_column: PreprocessedColumn) -> None:
         for metric in self._metrics.values():