[
https://issues.apache.org/jira/browse/COLLECTIONS-800?focusedWorklogId=698182&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-698182
]
ASF GitHub Bot logged work on COLLECTIONS-800:
----------------------------------------------
Author: ASF GitHub Bot
Created on: 18/Dec/21 02:19
Start Date: 18/Dec/21 02:19
Worklog Time Spent: 10m
Work Description: 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
##########
@@ -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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Issue Time Tracking
-------------------
Worklog Id: (was: 698182)
Time Spent: 40m (was: 0.5h)
> Provide a ListUtils.partitionBalanced(List, int) method where returned
> sublists are "balanced"
> ----------------------------------------------------------------------------------------------
>
> Key: COLLECTIONS-800
> URL: https://issues.apache.org/jira/browse/COLLECTIONS-800
> Project: Commons Collections
> Issue Type: New Feature
> Components: List
> Reporter: Claudio
> Priority: Minor
> Time Spent: 40m
> Remaining Estimate: 0h
>
> [https://github.com/apache/commons-collections/pull/265]
> The new method re-uses some of the logic of the existing
> ListUtils.partition(List, int). The difference with that method is that the
> returned sublists are "balanced" so that they all have the same amount of
> elements (with a maximum of 1 element difference). Some examples:
> A list of 10 elements, partition 10:
> * partition() and partitionBalanced() both return a single sublist with 10
> elements
> A list of 11 elements, partition 10:
> * partition() returns a sublist of 10 and another sublist of 1 element
> * partitionBalanced() method returns a sublist of 6 and another sublist of 5
> elements
> A list of 14 elements, partition 10:
> * partition() returns a sublist of 10 and another sublist of 4 elements
> * partitionBalanced() method returns two sublists of 7 elements each
> A list of 20 elements, partition 10:
> * partition() and partitionBalanced() both return two sublists of 10 elements
>
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