Github user fhueske commented on a diff in the pull request:
https://github.com/apache/incubator-flink/pull/244#discussion_r21091377
--- Diff: flink-java/src/main/java/org/apache/flink/api/java/DataSet.java
---
@@ -348,45 +360,75 @@ public ExecutionEnvironment getExecutionEnvironment()
{
}
/**
- * Applies a special case of a reduce transformation (minBy) on a
non-grouped {@link DataSet}.<br/>
- * The transformation consecutively calls a {@link ReduceFunction}
- * until only a single element remains which is the result of the
transformation.
- * A ReduceFunction combines two elements into one new element of the
same type.
- *
- * @param fields Keys taken into account for finding the minimum.
- * @return A {@link ReduceOperator} representing the minimum.
+ * Selects an element with minimum value.
+ * <p>
+ * The maximum is computed over the specified fields in lexicographical
order.
+ * <p>
+ * <strong>Example 1</strong>: Given a data set with elements <code>[0,
1], [1, 0]</code>, the
+ * results will be:
+ * <ul>
+ * <li><code>minBy(0)</code>: <code>[0, 1]</code></li>
+ * <li><code>minBy(1)</code>: <code>[1, 0]</code></li>
+ * </ul>
+ * <p>
+ * <strong>Example 2</strong>: Given a data set with elements <code>[0,
0], [0, 1]</code>, the
+ * results will be:
+ * <ul>
+ * <li><code>minBy(0, 1)</code>: <code>[0, 0]</code></li>
+ * </ul>
+ * <p>
+ * If multiple values with minimum value at the specified fields exist,
the first one will be
+ * picked.
+ * <p>
+ * Internally, this operation is implemented as a {@link
ReduceFunction}.
+ *
+ * @param fields Field positions to compute the minimum over
+ * @return A {@link ReduceOperator} representing the minimum
*/
@SuppressWarnings({ "unchecked", "rawtypes" })
public ReduceOperator<T> minBy(int... fields) {
-
- // Check for using a tuple
- if(!this.type.isTupleType()) {
- throw new InvalidProgramException("Method minBy(int)
only works on tuples.");
+ if(!type.isTupleType()) {
+ throw new
InvalidProgramException("DataSet#minBy(int...) only works on Tuple types.");
}
-
+
return new ReduceOperator<T>(this, new SelectByMinFunction(
- (TupleTypeInfo) this.type, fields),
Utils.getCallLocationName());
+ (TupleTypeInfo) type, fields),
Utils.getCallLocationName());
}
/**
- * Applies a special case of a reduce transformation (maxBy) on a
non-grouped {@link DataSet}.<br/>
- * The transformation consecutively calls a {@link ReduceFunction}
- * until only a single element remains which is the result of the
transformation.
- * A ReduceFunction combines two elements into one new element of the
same type.
- *
- * @param fields Keys taken into account for finding the minimum.
- * @return A {@link ReduceOperator} representing the minimum.
+ * Selects an element with maximum value.
+ * <p>
+ * The maximum is computed over the specified fields in lexicographical
order.
+ * <p>
+ * <strong>Example 1</strong>: Given a data set with elements <code>[0,
1], [1, 0]</code>, the
+ * results will be:
+ * <ul>
+ * <li><code>maxBy(0)</code>: <code>[1, 0]</code></li>
+ * <li><code>maxBy(1)</code>: <code>[0, 1]</code></li>
+ * </ul>
+ * <p>
+ * <strong>Example 2</strong>: Given a data set with elements <code>[0,
0], [0, 1]</code>, the
+ * results will be:
+ * <ul>
+ * <li><code>maxBy(0, 1)</code>: <code>[0, 1]</code></li>
+ * </ul>
+ * <p>
+ * If multiple values with maximum value at the specified fields exist,
the first one will be
--- End diff --
as above.
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