Added heatmap slicing convenience for generating a heatmap with a particular height

Author: karwa

Sources/SwiftPlot/Heatmap.swift

@@ -173,14 +173,31 @@ extension RandomAccessCollection {
   public func heatmap(width: Int, interpolator: Interpolator<Element>) -> Heatmap<[SubSequence]> {
     precondition(width > 0, "Cannot build a histogram with zero or negative width")
     let height = Int((Float(count) / Float(width)).rounded(.up))
-    return (0..<height).map { row -> SubSequence in
-      guard let start = index(startIndex, offsetBy: row * width, limitedBy: endIndex) else {
-        return self[startIndex..<startIndex]
-      }
-      guard let end = index(start, offsetBy: width, limitedBy: endIndex) else {
-        return self[start..<endIndex]
-      }
-      return self[start..<end]
-    }.heatmap(interpolator: interpolator)
+    return (0..<height)
+      .map { _sliceForRow($0, width: width) }
+      .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]> {
+    precondition(height > 0, "Cannot build a histogram with zero or negative height")
+    let width = Int((Float(count) / Float(height)).rounded(.up))
+    return (0..<height)
+      .map { _sliceForRow($0, width: width) }
+      .heatmap(interpolator: interpolator)
+  }
+  
+  private func _sliceForRow(_ row: Int, width: Int) -> SubSequence {
+    guard let start = index(startIndex, offsetBy: row * width, limitedBy: endIndex) else {
+      return self[startIndex..<startIndex]
+    }
+    guard let end = index(start, offsetBy: width, limitedBy: endIndex) else {
+      return self[start..<endIndex]
+    }
+    return self[start..<end]
   }
 }

Tests/SwiftPlotTests/Heatmap/heatmap.swift

@@ -30,10 +30,10 @@ final class HeatmapTests: SwiftPlotTestCase {
 
     var d = Data(capacity: 10_000)
     for _ in 0..<10_000 { d.append(.random(in: 0..<255)) }
-    var hm3 = d.heatmap(width: 100, interpolator: .linear)
+//    var hm3 = d.heatmap(width: 100, interpolator: .linear)
 
-//    var hm3 = Array("THIS IS SWIFPLOT!!!! Woo let's see what this looks like :)")
-//      .heatmap(width: 5, interpolator: .linearByKeyPath(\.asciiValue!))
+    var hm3 = Array("THIS IS SWIFPLOT!!!! Woo let's see what this looks like :)")
+      .heatmap(height: 1, interpolator: .linearByKeyPath(\.asciiValue!))
 //    var hm3 = Array(stride(from: Float(0), to: 1, by: 0.001)).heatmap(width: 10, interpolator: .linear)
     hm3.colorMap = .viridis