small test

src/histogram.rs

@@ -34,6 +34,11 @@ impl Bin<f32> {
         }
     }
 
+    pub fn update(&mut self, gradient_sum: f32, hessian_sum: f32) {
+        self.gradient_sum = gradient_sum;
+        self.hessian_sum = hessian_sum;
+    }
+
     /// Calculate a new bin, using the subtraction trick when the parent node
     /// has three directions, left, right, and missing.
     pub fn from_parent_two_children(
@@ -85,25 +90,37 @@ pub fn create_feature_histogram(
     index: &[usize],
 ) -> Vec<Bin<f32>> {
     let mut histogram: Vec<Bin<f64>> = Vec::with_capacity(cuts.len());
-    // The first value is missing, it seems to not matter that we are using
-    // Missing here, rather than the booster "missing" definition, because
-    // we just always assume the first bin of the histogram is missing.
-    histogram.push(Bin::new_f64(f64::NAN));
+
+    let mut gradient_sums: Vec<f64> = Vec::with_capacity(cuts.len());
+    let mut hessian_sums: Vec<f64> = Vec::with_capacity(cuts.len());
+
+    histogram.push(Bin::new_f32(f64::NAN));
     // The last cut value is simply the maximum possible value, so we don't need it.
     // This value is needed initially for binning, but we don't need to count it as
     // a histogram bin.
-    histogram.extend(cuts[..(cuts.len() - 1)].iter().map(|c| Bin::new_f64(*c)));
+    histogram.extend(cuts[..(cuts.len() - 1)].iter().map(|c| Bin::new_f32(*c)));
+
     index
         .iter()
         .zip(sorted_grad)
         .zip(sorted_hess)
         .for_each(|((i, g), h)| {
-            if let Some(v) = histogram.get_mut(feature[*i] as usize) {
-                v.gradient_sum += f64::from(*g);
-                v.hessian_sum += f64::from(*h);
+            if let Some(v) = gradient_sums.get_mut(feature[*i] as usize) {
+                *v += f64::from(*g);
+            }
+            if let Some(v) = hessian_sums.get_mut(feature[*i] as usize) {
+                *v += f64::from(*h);
             }
         });
-    histogram.iter().map(|b| b.as_f32_bin()).collect()
+    // The last cut value is simply the maximum possible value, so we don't need it.
+    // This value is needed initially for binning, but we don't need to count it as
+    // a histogram bin.
+    histogram
+        .iter_mut()
+        .zip(gradient_sums)
+        .zip(hessian_sums)
+        .map(|(h, (g, h))| h.update(g, h))
+        .collect()
 }
 
 impl HistogramMatrix {