Github user decibel commented on a diff in the pull request:
https://github.com/apache/incubator-madlib/pull/47#discussion_r67944965
--- Diff: src/ports/postgres/modules/utilities/pivot.sql_in ---
@@ -0,0 +1,202 @@
+/* -----------------------------------------------------------------------
*//**
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ *
+ * @file pivot.sql_in
+ *
+ * @brief SQL functions for pivoting
+ * @date June 2014
+ *
+ * @sa Creates a pivot table for data summarization.
+ *
+ *//*
----------------------------------------------------------------------- */
+
+m4_include(`SQLCommon.m4')
+
+/**
+@addtogroup grp_pivot
+
+<div class="toc"><b>Contents</b>
+<ul>
+<li><a href="#categorical">Pivoting</a></li>
+<li><a href="#notes">Notes</a></li>
+<li><a href="#examples">Examples</a></li>
+</ul>
+</div>
+
+@brief Provides pivoting functions helpful for data preparation before
modeling
+
+@anchor categorical
+The goal of the MADlib pivot function is to provide a data summarization
tool
+that can do basic OLAP type operations on data stored in one table and
output
+the summarized data to a second table.
+
+
+<pre class="syntax">
+pivot(
+ source_table,
+ out_table,
+ index,
+ pivot_cols,
+ pivot_values
+ )
+</pre>
+\b Arguments
+<dl class="arglist">
+ <dt>source_table</dt>
+ <dd>VARCHAR. Name of the source table, containing data for
pivoting.</dd>
+ <dt>output_table</dt>
+ <dd>VARCHAR. Name of output table taht contains pivoted data.
+ The output table ('output_table' above) has all the columns present in
+ index column list, plus additional columns for each distinct value in
+ pivot_cols. The column name for the pivot is set as
+ <em>'pivot name'</em>_<em>'pivot value'</em>.
+ </dd>
+ <dt>index </dt>
+ <dd>VARCHAR. Comma-separated columns that will form the index of the
output
+ pivot table.</dd>
+ <dt>pivot_cols </dt>
+ <dd>VARCHAR. Comma-separated columns that will form the columns of the
+ output pivot table.</dd>
+ <dt>pivot_values </dt>
+ <dd>VARCHAR. Comma-separated columns that contain the values to be
+ summarized in the output pivot table.</dd>
+
+</dl>
+
+@anchor notes
+@par Notes
+
+The default aggregate function is "sum".
+
+NULL values in the index column are treated as any other value.
+
+NULL values in the pivot column are ignored.
+
+NULL values in the value column are handled by the aggregate function.
+
+The following features are planned but not yet implemented.
+
+- Multiple index columns.
+- Multiple pivot columns.
+- Multiple value columns.
+- Aggregate functions as input.
+- NULL values in the pivot.
+
+
+@anchor examples
+@examp
+
+-# Create a toy dataset.
+<pre class="example">
+CREATE TABLE pivset(
+ id INTEGER,
+ piv FLOAT8,
+ val FLOAT8
+ );
+INSERT INTO pivset VALUES
+ (0, 10, 1),
+ (0, 10, 2),
+ (0, 20, 3),
+ (1, 20, 4),
+ (1, 30, 5),
+ (1, 30, 6),
+ (1, 10, 7),
+ (NULL, 10, 8),
+ (1, NULL, 9),
+ (1, 10, NULL);
+</pre>
+
+-# Pivot the table
+<pre class="example">
+DROP TABLE IF EXISTS pivout;
+SELECT madlib.pivot('pivset', 'pivout', 'id', 'piv', 'val');
+SELECT * FROM pivout;
+</pre>
+<pre class="result">
+ id | piv_10.0 | piv_20.0 | piv_30.0
+------+------------+------------+------------
+ 0 | 3 | 3 |
+ 1 | 7 | 4 | 11
+ | 8 | 0 | 0
+</pre>
+*/
+
+-------------------------------------------------------------------------
+
+
+/**
+ * @brief Helper function that can be used to pivot tables
+ *
+ * @param source_table The original data table
+ * @param out_table The output table that contains the dummy
+ * variable columns
+ * @param index The index columns to group by the records by
+ * @param pivot_cols The columns to pivot the table
+ * @param pivot_values The value columns to be summarized in the
+ * pivoted table
+ * @param aggregate_func The aggregate function to be applied to the
+ * values
+ *
+ * @return Void
+ *
+ */
+
+CREATE OR REPLACE FUNCTION MADLIB_SCHEMA.pivot(
+ source_table TEXT,
+ out_table TEXT,
+ index TEXT,
+ pivot_cols TEXT,
+ pivot_values TEXT,
+ aggregate_func TEXT
+
+) RETURNS VOID AS $$
+ PythonFunction(utilities, pivot, pivot)
+$$ LANGUAGE plpythonu
+m4_ifdef(`__HAS_FUNCTION_PROPERTIES__', `MODIFIES SQL DATA', `');
+
+CREATE OR REPLACE FUNCTION MADLIB_SCHEMA.pivot(
--- End diff --
Instead of overloading the functions, it would be clearer to use default
values for the parameters.
Though, it might be best to keep the "help" version separate; so add a
default value for aggregate_func above, and then have a single argument version
where the default value for the first argument is 'help'.
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