Github user hyunsik commented on a diff in the pull request:
https://github.com/apache/tajo/pull/231#discussion_r20972854
--- Diff: tajo-common/src/main/java/org/apache/tajo/util/TUtil.java ---
@@ -258,4 +258,30 @@ public static String getCurrentCodePoint(final int
depth) {
StackTraceElement element = ste[2 + depth];
return element.getClassName() + ":" + element.getMethodName() + "(" +
element.getLineNumber() +")";
}
+
+ /**
+ * It returns every subsets of the given original set.
+ *
+ * @param originalSet an input set
+ * @param <T> the type of elements of the input set
+ * @return every subsets of the given original set.
+ */
+ public static <T> List<List<T>> powerSet(List<T> originalSet) {
--- End diff --
It looks good. BTW, you also can use ```Sets.powerSet()``` method.
http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Sets.html#powerSet(java.util.Set)
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