Github user dbtsai commented on a diff in the pull request:
https://github.com/apache/spark/pull/8079#discussion_r36717693
--- Diff:
mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala
---
@@ -43,36 +42,60 @@ import org.apache.spark.storage.StorageLevel
*/
private[classification] trait LogisticRegressionParams extends
ProbabilisticClassifierParams
with HasRegParam with HasElasticNetParam with HasMaxIter with
HasFitIntercept with HasTol
- with HasStandardization {
+ with HasStandardization with HasThreshold {
/**
- * Version of setThresholds() for binary classification, available for
backwards
- * compatibility.
+ * Set threshold in binary classification prediction, in range [0, 1].
+ * If [[thresholds]] is set, then [[threshold]] is ignored.
*
- * Calling this with threshold p will effectively call
`setThresholds(Array(1-p, p))`.
+ * If the estimated probability of class label 1 is > threshold, then
predict 1, else 0.
+ * A high threshold encourages the model to predict 0 more often;
+ * a low threshold encourages the model to predict 1 more often.
*
- * Default is effectively 0.5.
+ * Note: Calling this with threshold p is equivalent to calling
`setThresholds(Array(1-p, p))`.
+ *
+ * Default is 0.5.
* @group setParam
*/
- def setThreshold(value: Double): this.type = set(thresholds, Array(1.0 -
value, value))
+ def setThreshold(value: Double): this.type
/**
- * Version of [[getThresholds()]] for binary classification, available
for backwards
- * compatibility.
+ * Get threshold for binary classification prediction.
+ * If [[thresholds]] is set, then [[threshold]] is ignored.
*
- * Param thresholds must have length 2 (or not be specified).
- * This returns {{{1 / (1 + thresholds(0) / thresholds(1))}}}.
+ * @return If [[thresholds]] is set with length 2 (i.e., binary
classification), this returns
+ * the equivalent threshold: {{{1 / (1 + thresholds(0) /
thresholds(1))}}}.
+ * Otherwise, returns [[threshold]] value.
* @group getParam
+ * @throws RuntimeException if [[thresholds]] is set to an array of
length other than 2.
*/
- def getThreshold: Double = {
- if (isDefined(thresholds)) {
+ override def getThreshold: Double = {
+ if (isSet(thresholds)) {
val thresholdValues = $(thresholds)
- assert(thresholdValues.length == 2, "Logistic Regression
getThreshold only applies to" +
- " binary classification, but thresholds has length != 2." +
- s" thresholds: ${thresholdValues.mkString(",")}")
+ if (thresholdValues.length != 2) {
+ throw new RuntimeException("Logistic Regression getThreshold only
applies to" +
+ " binary classification, but thresholds has length != 2.
thresholds: " +
+ thresholdValues.mkString(","))
+ }
1.0 / (1.0 + thresholdValues(0) / thresholdValues(1))
} else {
- 0.5
+ $(threshold)
+ }
+ }
+
+ /**
+ * If [[thresholds]] is set, return its value.
+ * Otherwise, if [[threshold]] is set, return the equivalent thresholds
for binary
+ * classification: (1-threshold, threshold).
+ * If neither are set, throw an exception.
+ * @group getParam
+ */
+ override def getThresholds: Array[Double] = {
--- End diff --
Seems that we are preferring thresholds now, and I agree that it will be
more flexible for multi-classes problem. However, users may set both of them
with different values mistakenly, or for a old param, users use `setThreshold`,
but now he switched to `setThresholds` which may cause some confusion. How
about we throw Exception when they are not agreed? Also, whenever one is set,
we just make the other unset.
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