Highlighter fix

[kcome]

Fixed the use of partitioningIndex(where:) in ChartDataSet.entriesForXValue
Fixed the rounding issue of ChartDataSet.entryIndex()

Issue Link 🔗

#4719

Goals ⚽

Having a working highlighter which is broken due to incorrect use of Algorithms partitioningIndex()

Implementation Details 🚧

Partition the entries first, then call partitioningIndex()

Testing Details 🔍

Using the attached ChartDemo-iOS-Swift project

Open LineChart1 or LineChart2, tap data points, highlight should work

[krzysztof-grobelny]

@kcome Hello! Would you mind sharing some explanation on that fix? I've noticed the defect shows up only after building Charts with Xcode 13, no?

[kcome]

@krzysztof-grobelny The issue #4719 happens on both Xcode 13 and 12.

There are two fixes together solves #4719 :

1 is in class ChartDataSet, function open override func entryIndex(x xValue: Double, closestToY yValue: Double, rounding: ChartDataSetRounding) -> Int. When using "closest" rounding method, there was no checking present. E.g. in data-set [(1,1), (2,2), (3,3)], when trying to find closest point to xValue 2.1 with closest rounding, previous solution gives (3, 3) but actually the closes point is (2,2).

2 is in open override func entriesForXValue(_ xValue: Double) -> [ChartDataEntry]. According to swift-algorithm document:

The partitioningIndex(where:) method returns the index of the start of the second partition when called on an already partitioned collection.

Previous implementation didn't call .partition(by: match) so the result of .partitioningIndex(where: match) is not what we want.

[mt-bsingh]

@kcome Thanks for the fix, @krzysztof-grobelny This issue happens on XCode12, In the demo code for ChartDemo-iOS-Swift. Some bars are selectable sometimes but definitely not all. This fix looks right to me. Same time I found out that's the problem.

[kcome]

@liuxuan30 could we merge this PR?

[kcome]

Hi @pmairoldi , I resolved a conflict in this PR. Could we start merge? Let me know if there is anything else need to be done.

[dudenamedjune]

Think I have a proper fix open for this #4817
#4719 (comment)

[417-72KI]

I tried with #4817 and seems to work chartValueSelected(_:entry:highlight:),
but chartValueNothingSelected(_:) still not worked.

This PR works both and seems to be expected specs ☺️

[pmairoldi]

Thanks! Seems to work fine.

[PWrzesinski]

I believe this line should be:

let match: (ChartDataEntry) -> Bool = { $0.x >= xValue }

Note the >= instead of ==.

[pmairoldi]

Can you explain why?

[PWrzesinski]

Actually nevermind, sorry for bothering you! Please disregard this and other comments - I'll delete them.

My thinking was that partitioningIndex function requires that all values after the desired index match the expression, but after looking more carefully I see the added partition function before running partitioningIndex - I'm guessing the intention is to make it possible to search in non-ordered data. I'm a little worried about the performance here, but otherwise I think the implementation is correct, except one detail: comparing Doubles directly. This is probably bigger discussion about the library design, but basically due to Double representation in memory, we should never compare Doubles using the equality operator. This will break for example in a simple case: 0.3 != 0.1 + 0.2. But as I said, that's probably a separate discussion.

[wlxo0401]

chartValueNothingSelected not work