- Namespace the Sequence heatmap APIs

- Limit rounding on heatmap to elements with size > 1

Author: karwa

Sources/SwiftPlot/Heatmap.swift

@@ -73,8 +73,15 @@ extension Heatmap: HasGraphLayout, Plot {
       width: size.width / Float(results.columns),
       height: size.height / Float(results.rows)
     )
-    results.itemSize.width.round(.down)
-    results.itemSize.height.round(.down)
+    // If we have at enough space to give each element a pixel,
+    // round the items down to integer dimensions to remove aliasing
+    // in the rendered image.
+    if results.itemSize.width > 1 {
+      results.itemSize.width = max(results.itemSize.width.rounded(.down), 1)
+    }
+    if results.itemSize.height > 1 {
+      results.itemSize.height = max(results.itemSize.height.rounded(.down), 1)
+    }
     // Calculate markers.
     markers.xMarkers = (0..<results.columns).map {
       (Float($0) + 0.5) * results.itemSize.width
@@ -154,18 +161,18 @@ extension Heatmap
 
 // Collection construction shorthand.
 
-extension Sequence where Element: Sequence {
+extension SequencePlots where Base.Element: Sequence {
 
   /// Returns a heatmap of values from this 2-dimensional sequence.
   /// - parameters:
   ///   - interpolator: A function or `KeyPath` which maps values to a continuum between 0 and 1.
   /// - returns: A heatmap plot of the sequence's inner items.
-  public func heatmap(interpolator: Interpolator<Element.Element>) -> Heatmap<Self> {
-    return Heatmap(values: self, interpolator: interpolator)
+  public func heatmap(interpolator: Interpolator<Base.Element.Element>) -> Heatmap<Base> {
+    return Heatmap(values: base, interpolator: interpolator)
   }
 }
 
-extension Collection {
+extension SequencePlots where Base: Collection {
 
   /// Returns a heatmap of this collection's values, generated by slicing rows with the given width.
   /// - parameters:
@@ -174,51 +181,53 @@ extension Collection {
   /// - returns: A heatmap plot of the collection's values.
   /// - complexity: O(n). Consider though, that rendering a heatmap or copying to a `RamdomAccessCollection`
   ///               is also at least O(n), and this does not copy the data.
-  public func heatmap(width: Int, interpolator: Interpolator<Element>) -> Heatmap<[SubSequence]> {
+  public func heatmap(width: Int, interpolator: Interpolator<Base.Element>) -> Heatmap<[Base.SubSequence]> {
     precondition(width > 0, "Cannot build a histogram with zero or negative width")
-    var rows = [SubSequence]()
-    var rowStart = startIndex
-    while rowStart != endIndex {
-      guard let rowEnd = index(rowStart, offsetBy: width, limitedBy: endIndex) else {
-        rows.append(self[rowStart..<endIndex])
+    var rows = [Base.SubSequence]()
+    var rowStart = base.startIndex
+    while rowStart != base.endIndex {
+      guard let rowEnd = base.index(rowStart, offsetBy: width, limitedBy: base.endIndex) else {
+        rows.append(base[rowStart..<base.endIndex])
         break
       }
-      rows.append(self[rowStart..<rowEnd])
+      rows.append(base[rowStart..<rowEnd])
       rowStart = rowEnd
     }
-    return rows.heatmap(interpolator: interpolator)
+    return rows.plots.heatmap(interpolator: interpolator)
   }
 }
 
-extension RandomAccessCollection {
+extension SequencePlots where Base: RandomAccessCollection {
 
   /// Returns a heatmap of this collection's values, generated by slicing rows with the given width.
   /// - parameters:
   ///   - width:        The width of the heatmap to generate. Must be greater than 0.
   ///   - interpolator: A function or `KeyPath` which maps values to a continuum between 0 and 1.
   /// - returns: A heatmap plot of the collection's values.
-  public func heatmap(width: Int, interpolator: Interpolator<Element>) -> Heatmap<[SubSequence]> {
+  public func heatmap(width: Int, interpolator: Interpolator<Base.Element>) -> Heatmap<[Base.SubSequence]> {
     precondition(width > 0, "Cannot build a histogram with zero or negative width")
-    let height = Int((Float(count) / Float(width)).rounded(.up))
+    let height = Int((Float(base.count) / Float(width)).rounded(.up))
     return (0..<height)
-      .map { _sliceForRow($0, width: width) }
-      .heatmap(interpolator: interpolator)
+      .map { base._sliceForRow($0, width: width) }
+      .plots.heatmap(interpolator: interpolator)
   }
 
   /// Returns a heatmap of this collection's values, generated by the data in to `height` rows.
   /// - parameters:
   ///   - height:        The height of the heatmap to generate. Must be greater than 0.
   ///   - interpolator: A function or `KeyPath` which maps values to a continuum between 0 and 1.
   /// - returns: A heatmap plot of the collection's values.
-  public func heatmap(height: Int, interpolator: Interpolator<Element>) -> Heatmap<[SubSequence]> {
+  public func heatmap(height: Int, interpolator: Interpolator<Base.Element>) -> Heatmap<[Base.SubSequence]> {
     precondition(height > 0, "Cannot build a histogram with zero or negative height")
-    let width = Int((Float(count) / Float(height)).rounded(.up))
+    let width = Int((Float(base.count) / Float(height)).rounded(.up))
     return (0..<height)
-      .map { _sliceForRow($0, width: width) }
-      .heatmap(interpolator: interpolator)
+      .map { base._sliceForRow($0, width: width) }
+      .plots.heatmap(interpolator: interpolator)
   }
-  
-  private func _sliceForRow(_ row: Int, width: Int) -> SubSequence {
+}
+
+extension RandomAccessCollection {
+  fileprivate func _sliceForRow(_ row: Int, width: Int) -> SubSequence {
     guard let start = index(startIndex, offsetBy: row * width, limitedBy: endIndex) else {
       return self[startIndex..<startIndex]
     }

Sources/SwiftPlot/SequencePlots.swift

@@ -0,0 +1,12 @@
+
+/// A namespace for graphs which may be drawn from this sequence.
+public struct SequencePlots<Base> where Base: Sequence {
+  var base: Base
+}
+
+extension Sequence {
+  /// Graphs which may be drawn from this sequence.
+  public var plots: SequencePlots<Self> {
+    return SequencePlots(base: self)
+  }
+}