LarsBodewig commented on a change in pull request #265:
URL:
https://github.com/apache/commons-collections/pull/265#discussion_r771769961
##########
File path: src/main/java/org/apache/commons/collections4/ListUtils.java
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@@ -117,9 +119,25 @@ private Partition(final List<T> list, final int size) {
throw new IndexOutOfBoundsException("Index " + index + " must
be less than size " +
listSize);
}
- final int start = index * size;
- final int end = Math.min(start + size, list.size());
- return list.subList(start, end);
+ int start;
+ int currentPartitionSize;
+ if (isBalanced) {
+ // evenly distribute partitions
+ currentPartitionSize = (int) Math.ceil((double) list.size() /
(double) listSize);
+ start = index * currentPartitionSize;
+ // remainder of above is the threshold for which indices
greater than will have one less element
+ final int threshold = (list.size() % listSize);
+ // when currentPartitionSize is 1 or threshold is 0 there's
nothing to balance
+ // when index hasn't crossed the threshold we don't need
balancing yet
+ if (currentPartitionSize > 1 && threshold > 0 && index >=
threshold) {
+ start -= (index - threshold); // adjust start as
partitions before threshold have one less element
+ currentPartitionSize--; // currentPartitionSize is
decremented as threshold is crossed
Review comment:
Newbie myself, but I wonder if that could be written more simply:
```java
evenlyDistributedSize = ...
if (index < threshold) { // lists before threshold should contain +1
start = index * (evenlyDistributedSize + 1);
end = start + (evenlyDistributedSize + 1);
} else {
start = index * evenlyDistributedSize + threshold; // offset other
starting positions by threshold
end = start + evenlyDistributedSize;
}
```
...or similar (Note: this is untested). The if condition and subtractions
look quite complicated in my opinion.
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