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diff --git a/core/src/main/scala/org/apache/spark/partial/StudentTCacher.scala b/core/src/main/scala/org/apache/spark/partial/StudentTCacher.scala
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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 org.apache.spark.partial
+
+import cern.jet.stat.Probability
+
+/**
+ * A utility class for caching Student's T distribution values for a given confidence level
+ * and various sample sizes. This is used by the MeanEvaluator to efficiently calculate
+ * confidence intervals for many keys.
+ */
+private[spark] class StudentTCacher(confidence: Double) {
+  val NORMAL_APPROX_SAMPLE_SIZE = 100  // For samples bigger than this, use Gaussian approximation
+  val normalApprox = Probability.normalInverse(1 - (1 - confidence) / 2)
+  val cache = Array.fill[Double](NORMAL_APPROX_SAMPLE_SIZE)(-1.0)
+
+  def get(sampleSize: Long): Double = {
+    if (sampleSize >= NORMAL_APPROX_SAMPLE_SIZE) {
+      normalApprox
+    } else {
+      val size = sampleSize.toInt
+      if (cache(size) < 0) {
+        cache(size) = Probability.studentTInverse(1 - confidence, size - 1)
+      }
+      cache(size)
+    }
+  }
+}