Backport np helper functions to geotrellis.util.np

- linspace: https://docs.scipy.org/doc/numpy/reference/generated/numpy.linspace.html
- percentile: https://docs.scipy.org/doc/numpy/reference/generated/numpy.percentile.html

Also adds implicit helper methods for Tile.percentile

project/Settings.scala

@@ -610,6 +610,7 @@ object Settings {
     libraryDependencies ++= Seq(
       logging,
       pureconfig,
+      spire,
       scalatest % Test
     )
   )

raster/src/main/scala/geotrellis/raster/Implicits.scala

@@ -17,9 +17,9 @@
 package geotrellis.raster
 
 import geotrellis.vector.Point
-import geotrellis.macros.{ NoDataMacros, TypeConversionMacros }
+import geotrellis.macros.{NoDataMacros, TypeConversionMacros}
 import geotrellis.vector._
-import geotrellis.util.MethodExtensions
+import geotrellis.util.{MethodExtensions, np}
 
 
 object Implicits extends Implicits
@@ -98,4 +98,32 @@ trait Implicits
           s"${t._1.dimensions} does not match ${t._2.dimensions}")
       }
   }
+
+  implicit class TilePercentileExtensions(tile: Tile) {
+    /**
+      * Compute percentile at the given breaks using the same algorithm as numpy
+      *
+      * https://docs.scipy.org/doc/numpy/reference/generated/numpy.percentile.html
+      * https://en.wikipedia.org/wiki/Percentile
+      *
+      * @param pctBreaks
+      * @return
+      */
+    def percentile(pctBreaks: Array[Double]): Array[Double] = {
+      np.percentile(tile.toArrayDouble.filter(isData(_)), pctBreaks)
+    }
+
+    /**
+      * Compute percentile at the given break using the same algorithm as numpy
+      *
+      * https://docs.scipy.org/doc/numpy/reference/generated/numpy.percentile.html
+      * https://en.wikipedia.org/wiki/Percentile
+      *
+      * @param pctBreak
+      * @return
+      */
+    def percentile(pctBreak: Double): Double = {
+      np.percentile(tile.toArrayDouble.filter(isData(_)), pctBreak)
+    }
+  }
 }

raster/src/test/scala/geotrellis/raster/TileSpec.scala

@@ -383,4 +383,20 @@ class TileSpec extends FunSpec
                                  2, 3, 4, 2))
     }
   }
+
+  describe("percentile") {
+    it("should construct a numpy percentile for a Tile") {
+      val x = ArrayTile((0 until 8).map(_ * 0.5).toArray, 7, 1)
+
+      x.percentile(0) shouldBe 0d
+      x.percentile(100) shouldBe 3.5
+      x.percentile(50) shouldBe 1.75
+
+      val xmutable = x.mutable
+      xmutable.setDouble(1, 0, NODATA)
+      val xn = xmutable.toArrayTile
+
+      xn.percentile(0) shouldBe NODATA
+    }
+  }
 }

util/src/main/scala/geotrellis/util/np/package.scala

@@ -0,0 +1,87 @@
+/*
+ * Copyright 2019 Azavea
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package geotrellis.util
+
+import spire.syntax.cfor.cfor
+
+package object np {
+
+  /**
+    * Return evenly spaced numbers over the specified interval
+    * @param min Min bound of the interval, inclusive
+    * @param max Max bound of the interval, inclusive
+    * @param points Number of samples to generate
+    * @return
+    */
+  def linspace(min: Double, max: Double, points: Int): Array[Double] = {
+    val d = new Array[Double](points)
+    cfor(0)(_ < points, _ + 1) { i =>
+      d(i) = min + i * (max - min) / (points - 1)
+    }
+    d
+  }
+
+  /**
+    * Compute percentile at the given breaks using the same algorithm as numpy
+    *
+    * https://docs.scipy.org/doc/numpy/reference/generated/numpy.percentile.html
+    * https://en.wikipedia.org/wiki/Percentile
+    *
+    * @param data
+    * @param pctBreaks
+    * @return
+    */
+  def percentile(data: Array[Double],
+                 pctBreaks: Array[Double]): Array[Double] = {
+    // TODO: Include the isData filter check in the Tile implicit method
+    // val arr = data.filter(isData(_))
+    if (data.nonEmpty) {
+      val length = data.length
+      val sorted = data.sorted
+      if (length == 1) {
+        Array(data(0))
+      } else {
+        pctBreaks.map { break =>
+          val n = (break / 100d) * (length - 1d) + 1d
+          val k = math.floor(n).toInt
+          val d = n - k
+          if (k <= 0) {
+            sorted(0)
+          } else if (k >= length) {
+            sorted.last
+          } else {
+            sorted(k - 1) + d * (sorted(k) - sorted(k - 1))
+          }
+        }
+      }
+    } else {
+      Array()
+    }
+  }
+
+  /**
+    * Helper to compute percentile at a single break.
+    *
+    * See [[percentile(data: Array[Double], pctBreaks: Array[Double])]]
+    *
+    * @param data
+    * @param break
+    * @return
+    */
+  def percentile(data: Array[Double], break: Double): Double =
+    percentile(data, Array(break))(0)
+}

util/src/test/scala/geotrellis/util/np/LinspaceSpec.scala

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2019 Azavea
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package geotrellis.util.np
+
+import spire.syntax.cfor._
+import org.scalatest._
+
+class LinspaceSpec extends FunSpec with Matchers {
+
+  val pyArr =
+    Array(0d, 0.390625, 0.78125, 1.171875, 1.5625, 1.953125,
+      2.34375, 2.734375, 3.125, 3.515625, 3.90625, 4.296875,
+      4.6875, 5.078125, 5.46875, 5.859375, 6.25, 6.640625,
+      7.03125, 7.421875, 7.8125, 8.203125, 8.59375, 8.984375,
+      9.375, 9.765625, 10.15625, 10.546875, 10.9375, 11.328125,
+      11.71875, 12.109375, 12.5, 12.890625, 13.28125, 13.671875,
+      14.0625, 14.453125, 14.84375, 15.234375, 15.625, 16.015625,
+      16.40625, 16.796875, 17.1875, 17.578125, 17.96875, 18.359375,
+      18.75, 19.140625, 19.53125, 19.921875, 20.3125, 20.703125,
+      21.09375, 21.484375, 21.875, 22.265625, 22.65625, 23.046875,
+      23.4375, 23.828125, 24.21875, 24.609375, 25d, 25.390625,
+      25.78125, 26.171875, 26.5625, 26.953125, 27.34375, 27.734375,
+      28.125, 28.515625, 28.90625, 29.296875, 29.6875, 30.078125,
+      30.46875, 30.859375, 31.25, 31.640625, 32.03125, 32.421875,
+      32.8125, 33.203125, 33.59375, 33.984375, 34.375, 34.765625,
+      35.15625, 35.546875, 35.9375, 36.328125, 36.71875, 37.109375,
+      37.5, 37.890625, 38.28125, 38.671875, 39.0625, 39.453125,
+      39.84375, 40.234375, 40.625, 41.015625, 41.40625, 41.796875,
+      42.1875, 42.578125, 42.96875, 43.359375, 43.75, 44.140625,
+      44.53125, 44.921875, 45.3125, 45.703125, 46.09375, 46.484375,
+      46.875, 47.265625, 47.65625, 48.046875, 48.4375, 48.828125,
+      49.21875, 49.609375, 50d, 50.390625, 50.78125, 51.171875,
+      51.5625, 51.953125, 52.34375, 52.734375, 53.125, 53.515625,
+      53.90625, 54.296875, 54.6875, 55.078125, 55.46875, 55.859375,
+      56.25, 56.640625, 57.03125, 57.421875, 57.8125, 58.203125,
+      58.59375, 58.984375, 59.375, 59.765625, 60.15625, 60.546875,
+      60.9375, 61.328125, 61.71875, 62.109375, 62.5, 62.890625,
+      63.28125, 63.671875, 64.0625, 64.453125, 64.84375, 65.234375,
+      65.625, 66.015625, 66.40625, 66.796875, 67.1875, 67.578125,
+      67.96875, 68.359375, 68.75, 69.140625, 69.53125, 69.921875,
+      70.3125, 70.703125, 71.09375, 71.484375, 71.875, 72.265625,
+      72.65625, 73.046875, 73.4375, 73.828125, 74.21875, 74.609375,
+      75d, 75.390625, 75.78125, 76.171875, 76.5625, 76.953125,
+      77.34375, 77.734375, 78.125, 78.515625, 78.90625, 79.296875,
+      79.6875, 80.078125, 80.46875, 80.859375, 81.25, 81.640625,
+      82.03125, 82.421875, 82.8125, 83.203125, 83.59375, 83.984375,
+      84.375, 84.765625, 85.15625, 85.546875, 85.9375, 86.328125,
+      86.71875, 87.109375, 87.5, 87.890625, 88.28125, 88.671875,
+      89.0625, 89.453125, 89.84375, 90.234375, 90.625, 91.015625,
+      91.40625, 91.796875, 92.1875, 92.578125, 92.96875, 93.359375,
+      93.75, 94.140625, 94.53125, 94.921875, 95.3125, 95.703125,
+      96.09375, 96.484375, 96.875, 97.265625, 97.65625, 98.046875,
+      98.4375, 98.828125, 99.21875, 99.609375
+    )
+
+  describe("linspace should behave like numpy.linspace") {
+    it("linspace [0; 100) with 255 points") {
+      val actual = linspace(0, 100, 256) // should contain theSameElementsAs pyArr
+      cfor(0)(_ < actual.length, _ + 1) { i =>
+        actual(i) shouldBe (pyArr(i) +- 4e-1) // math differs a bit from the py math
+      }
+    }
+  }
+}

util/src/test/scala/geotrellis/util/np/PercentileSpec.scala

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2019 Azavea
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package geotrellis.util.np
+
+import org.scalatest._
+
+class PercentileSpec extends FunSpec with Matchers {
+  // https://github.com/numpy/numpy/blob/b57957c639ca7c96c328003cc2436a06f8ecf9db/numpy/lib/tests/test_function_base.py#L2508
+  describe("percentile should behave like numpy.percentile") {
+    it("test basic") {
+      val x = (0 until 8).map(_ * 0.5).toArray
+
+      percentile(x, 0) shouldBe 0d
+      percentile(x, 100) shouldBe 3.5
+      percentile(x, 50) shouldBe 1.75
+    }
+  }
+}