fix issue with column name not always being present given the inputs, add more examples

Author: ehinman

dataretrieval/waterdata/api.py

@@ -1836,6 +1836,28 @@ def get_por_stats(
         individual rows in the dataframe. Missing percentile values expressed
         as 'nan' in the list of string values are removed from the dataframe
         to save space.
+
+    Examples
+    --------
+    .. code::
+
+        >>> # Get daily, monthly, and annual percentiles for streamflow at
+        >>> # a monitoring location of interest
+        >>> df, md = dataretrieval.waterdata.get_por_stats(
+        ...     monitoring_location_id="USGS-05114000",
+        ...     parameter_code="00060",
+        ...     computation_type="percentile"
+        ... )
+
+        >>> # Get all daily and monthly statistics for the month of January
+        >>> # over the entire period of record for streamflow and gage height
+        >>> # at a monitoring location of interest
+        >>> df, md = dataretrieval.waterdata.get_por_stats(
+        ...     monitoring_location_id="USGS-05114000",
+        ...     parameter_code=["00060", "00065"],
+        ...     start_date="01-01",
+        ...     end_date="01-31"
+        ... )
     """
     params = {
         k: v

dataretrieval/waterdata/utils.py

@@ -913,7 +913,7 @@ def _expand_percentiles(df: pd.DataFrame) -> pd.DataFrame:
             percentiles_explode = percentiles_explode.drop(columns=['values', 'percentiles'])
 
             # Merge exploded values back to other metadata/geometry
-            percentiles = percentiles.drop(columns=['values', 'percentiles', 'value']).merge(percentiles_explode, on='computation_id', how='left')
+            percentiles = percentiles.drop(columns=['values', 'percentiles', 'value'], errors="ignore").merge(percentiles_explode, on='computation_id', how='left')
 
             # Concatenate back to original
             dfs = pd.concat([df.loc[df['computation'] != "percentile"], percentiles]).drop(columns=['values', 'percentiles'])