Github user feynmanliang commented on a diff in the pull request:
https://github.com/apache/spark/pull/8197#discussion_r37345734
--- Diff: docs/ml-linear-methods.md ---
@@ -118,12 +133,114 @@ lrModel = lr.fit(training)
print("Weights: " + str(lrModel.weights))
print("Intercept: " + str(lrModel.intercept))
{% endhighlight %}
+</div>
</div>
+The `spark.ml` implementation of logistic regression also supports
+extracting a summary of the model over the training set. Note that the
+predictions and metrics which are stored as `Datafram`s in
+`BinaryLogisticRegressionSummary` are annoted `@transient` and hence
+only available on the driver.
+
+<div class="codetabs">
+
+<div data-lang="scala" markdown="1">
+
+[`LogisticRegressionTrainingSummary`](api/scala/index.html#org.apache.spark.ml.classification.LogisticRegressionTrainingSummary)
+provides a summary for a
+[`LogisticRegressionModel`](api/scala/index.html#org.apache.spark.ml.classification.LogisticRegressionModel).
+Currently, only binary classification is supported and the
+summary must be explicitly cast to
+[`BinaryLogisticRegressionTrainingSummary`](api/scala/index.html#org.apache.spark.ml.classification.BinaryLogisticRegressionTrainingSummary).
+This will likely change when multiclass classification is supported.
+
+Continuing the earlier example:
+
+{% highlight scala %}
+// Extract the summary from the returned LogisticRegressionModel instance
trained in the earlier example
+val trainingSummary = lrModel.summary
+
+// Obtain the loss per iteration.
+val objectiveHistory = trainingSummary.objectiveHistory
+objectiveHistory.foreach(loss => println(loss))
+
+// Obtain the metrics useful to judge performance on test data.
+// We cast the summary to a BinaryLogisticRegressionSummary since the
problem is a
+// binary classification problem.
+val binarySummary =
trainingSummary.asInstanceOf[BinaryLogisticRegressionSummary]
+
+// Obtain the receiver-operating characteristic as a dataframe and
areaUnderROC.
+val roc = binarySummary.roc
+roc.show()
+roc.select("FPR").show()
+println(binarySummary.areaUnderROC)
+
+// Get the threshold corresponding to the maximum F-Measure and rerun
LogisticRegression with
+// this selected threshold.
+val fMeasure = binarySummary.fMeasureByThreshold
+val maxFMeasure = fMeasure.select(max("F-Measure")).head().getDouble(0)
+val bestThreshold = fMeasure.where($"F-Measure" === maxFMeasure).
+ select("threshold").head().getDouble(0)
+logReg.setThreshold(bestThreshold)
+logReg.fit(logRegDataFrame)
+{% endhighlight %}
</div>
-### Optimization
+<div data-lang="java" markdown="1">
+[`LogisticRegressionTrainingSummary`](api/java/org/apache/spark/ml/classification/LogisticRegressionTrainingSummary.html)
+provides a summary for a
+[`LogisticRegressionModel`](api/java/org/apache/spark/ml/classification/LogisticRegressionModel.html).
+Currently, only binary classification is supported and the
+summary must be explicitly cast to
+[`BinaryLogisticRegressionTrainingSummary`](api/java/org/apache/spark/ml/classification/BinaryLogisticRegressionTrainingSummary.html).
+This will likely change when multiclass classification is supported.
+
+Continuing the earlier example:
+
+{% highlight java %}
+// Extract the summary from the returned LogisticRegressionModel instance
trained in the earlier example
+LogisticRegressionTrainingSummary trainingSummary = logRegModel.summary();
+
+// Obtain the loss per iteration.
+double[] objectiveHistory = trainingSummary.objectiveHistory();
+for (double lossPerIteration : objectiveHistory) {
--- End diff --
Nope, see [Google's Java Style
Guide](https://google.github.io/styleguide/javaguide.html#s4.6.2-horizontal-whitespace)
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