Another histogram refactor

kmath-histograms/src/commonMain/kotlin/space/kscience/kmath/histogram/UniformHistogram1D.kt

@@ -81,6 +81,30 @@ public class UniformHistogram1DGroup<V : Any, A>(
         builder.block()
         return UniformHistogram1D(this, map)
     }
+
+    /**
+     * Re-bin given histogram to be compatible if exiting bin fully falls inside existing bin, this bin value
+     * is increased by one. If not, all bins including values from this bin are increased by fraction
+     * (conserving the norming).
+     */
+    @UnstableKMathAPI
+    public fun produceFrom(histogram: Histogram1D<Double, V>): UniformHistogram1D<V> =
+        if ((histogram as? UniformHistogram1D)?.group == this) histogram
+        else {
+            val map = HashMap<Int, V>()
+            histogram.bins.forEach { bin ->
+                val range = bin.domain.range
+                val indexOfLeft = getIndex(range.start)
+                val indexOfRight = getIndex(range.endInclusive)
+                val numBins = indexOfRight - indexOfLeft + 1
+                for (i in indexOfLeft..indexOfRight) {
+                    map[indexOfLeft] = with(valueAlgebra) {
+                        (map[indexOfLeft] ?: zero) + bin.binValue / numBins
+                    }
+                }
+            }
+            UniformHistogram1D(this, map)
+        }
 }
 
 public fun <V : Any, A> Histogram.Companion.uniform1D(

kmath-histograms/src/commonTest/kotlin/space/kscience/kmath/histogram/UniformHistogram1DTest.kt

@@ -12,14 +12,15 @@ import space.kscience.kmath.misc.UnstableKMathAPI
 import space.kscience.kmath.operations.DoubleField
 import space.kscience.kmath.stat.RandomGenerator
 import space.kscience.kmath.stat.nextBuffer
+import kotlin.native.concurrent.ThreadLocal
 import kotlin.test.Test
 import kotlin.test.assertEquals
 
 @OptIn(ExperimentalCoroutinesApi::class, UnstableKMathAPI::class)
 internal class UniformHistogram1DTest {
+
     @Test
     fun normal() = runTest {
-        val generator = RandomGenerator.default(123)
         val distribution = NormalDistribution(0.0, 1.0)
         with(Histogram.uniform1D(DoubleField, 0.1)) {
             val h1 = produce(distribution.nextBuffer(generator, 10000))
@@ -31,4 +32,17 @@ internal class UniformHistogram1DTest {
             assertEquals(60000, h3.bins.sumOf { it.binValue }.toInt())
         }
     }
+
+    @Test
+    fun rebin() = runTest {
+        val h1 = Histogram.uniform1D(DoubleField, 0.1).produce(generator.nextDoubleBuffer(10000))
+        val h2 = Histogram.uniform1D(DoubleField,0.3).produceFrom(h1)
+
+        assertEquals(10000, h2.bins.sumOf { it.binValue }.toInt())
+    }
+
+    @ThreadLocal
+    companion object{
+        private val generator = RandomGenerator.default(123)
+    }
 }