From b6d505480a937276d92d5da766aa70e15008ce2d Mon Sep 17 00:00:00 2001
From: Ryan Ascheman <rascheman@groupon.com>
Date: Wed, 30 Oct 2019 15:39:27 -0700
Subject: [PATCH] add count function

---
 tdigest.go      |  9 +++++++++
 tdigest_test.go | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/tdigest.go b/tdigest.go
index e282f08..3de1c89 100644
--- a/tdigest.go
+++ b/tdigest.go
@@ -132,6 +132,15 @@ func (t *TDigest) Centroids() CentroidList {
 	return cl
 }
 
+func (t *TDigest) Count() float64 {
+	t.process()
+	count := 0.0
+	for _, centroid := range t.processed {
+		count += centroid.Weight
+	}
+	return count
+}
+
 func (t *TDigest) updateCumulative() {
 	if n := t.processed.Len() + 1; n <= cap(t.cumulative) {
 		t.cumulative = t.cumulative[:n]
diff --git a/tdigest_test.go b/tdigest_test.go
index 2d9b22f..2c7522e 100644
--- a/tdigest_test.go
+++ b/tdigest_test.go
@@ -47,6 +47,43 @@ func init() {
 	}
 }
 
+
+func TestTdigest_Count(t *testing.T) {
+	tests := []struct {
+		name     string
+		data     []float64
+		digest   *tdigest.TDigest
+		want     float64
+	}{
+		{
+			name:     "empty",
+			data:     []float64{},
+			want:     0,
+		},
+		{
+			name:     "not empty",
+			data:     []float64{5, 4},
+			want:     2,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			td := tt.digest
+			if td == nil {
+				td = tdigest.NewWithCompression(1000)
+				for _, x := range tt.data {
+					td.Add(x, 1)
+				}
+			}
+			got := td.Count()
+			if got != tt.want {
+				t.Errorf("unexpected count, got %g want %g", got, tt.want)
+			}
+		})
+	}
+}
+
 func TestTdigest_Quantile(t *testing.T) {
 	tests := []struct {
 		name     string