Fix for issue where data points are not highlighted

[gavynriebau]

Issue Link 🔗

Fixes #4609 and possibly also #4579

Goals ⚽

Improve the highlighting / selection behavior of line charts

Implementation Details 🚧

The entriesForXValue func finds the data entries for a given x-axis
value. It used an optimization where it would do a binary search to find
the first matching entry then take a slice of data stopping when no more
entries matched.

The optimization broke the highlight feature because data points that
should have matched were not matching resulting in no entries being
returned.

This commit replaces the optimized code with a call to .filter which
will be slower for larger data sets but correctly returns filtered
entries.

Testing Details 🔍

Tested by altering the demo project to use the forked version of the code and confirming the broken behaviour works after the fix is applied

[mlatham]

I also encountered this issue, so bump on this PR. I took a different approach to fixing it in our fork that I think addresses the regression while maintaining the optimized approach. The partitioningIndex just wasn't being calculated correctly.

/// - Returns: All Entry objects found at the given xIndex with binary search.
/// An empty array if no Entry object at that index.
open override func entriesForXValue(_ xValue: Double) -> [ChartDataEntry]
{
    let match: (ChartDataEntry) -> Bool = { $0.x == xValue }
    let i = partitioningIndex { $0.x >= xValue }
    guard i < endIndex else { return [] }
    return self[i...].prefix(while: match)
}

[gavynriebau]

@mlatham thanks for the code example, I tested out your fix and think you're correct it was just the filter predicate that was wrong.

In light of the above I'm closing this PR and have opened a simpler PR which still fixes the issue here:
#4613

[HWS123]

nice