[SPARK-11521][ML][DOC] Document that Logistic, Linear Regression summaries ignore weight col

Doc for 1.6 that the summaries mostly ignore the weight column.
To be corrected for 1.7

CC: mengxr thunterdb

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #9927 from jkbradley/linregsummary-doc.

mllib/src/main/scala/org/apache/spark/ml/classification/LogisticRegression.scala

@@ -755,23 +755,35 @@ class BinaryLogisticRegressionSummary private[classification] (
    * Returns the receiver operating characteristic (ROC) curve,
    * which is an Dataframe having two fields (FPR, TPR)
    * with (0.0, 0.0) prepended and (1.0, 1.0) appended to it.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    * @see http://en.wikipedia.org/wiki/Receiver_operating_characteristic
    */
   @transient lazy val roc: DataFrame = binaryMetrics.roc().toDF("FPR", "TPR")
 
   /**
    * Computes the area under the receiver operating characteristic (ROC) curve.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   lazy val areaUnderROC: Double = binaryMetrics.areaUnderROC()
 
   /**
    * Returns the precision-recall curve, which is an Dataframe containing
    * two fields recall, precision with (0.0, 1.0) prepended to it.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @transient lazy val pr: DataFrame = binaryMetrics.pr().toDF("recall", "precision")
 
   /**
    * Returns a dataframe with two fields (threshold, F-Measure) curve with beta = 1.0.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @transient lazy val fMeasureByThreshold: DataFrame = {
     binaryMetrics.fMeasureByThreshold().toDF("threshold", "F-Measure")
@@ -781,6 +793,9 @@ class BinaryLogisticRegressionSummary private[classification] (
    * Returns a dataframe with two fields (threshold, precision) curve.
    * Every possible probability obtained in transforming the dataset are used
    * as thresholds used in calculating the precision.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @transient lazy val precisionByThreshold: DataFrame = {
     binaryMetrics.precisionByThreshold().toDF("threshold", "precision")
@@ -790,6 +805,9 @@ class BinaryLogisticRegressionSummary private[classification] (
    * Returns a dataframe with two fields (threshold, recall) curve.
    * Every possible probability obtained in transforming the dataset are used
    * as thresholds used in calculating the recall.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LogisticRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @transient lazy val recallByThreshold: DataFrame = {
     binaryMetrics.recallByThreshold().toDF("threshold", "recall")

mllib/src/main/scala/org/apache/spark/ml/regression/LinearRegression.scala

@@ -540,6 +540,9 @@ class LinearRegressionSummary private[regression] (
    * Returns the explained variance regression score.
    * explainedVariance = 1 - variance(y - \hat{y}) / variance(y)
    * Reference: [[http://en.wikipedia.org/wiki/Explained_variation]]
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LinearRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @Since("1.5.0")
   val explainedVariance: Double = metrics.explainedVariance
@@ -547,6 +550,9 @@ class LinearRegressionSummary private[regression] (
   /**
    * Returns the mean absolute error, which is a risk function corresponding to the
    * expected value of the absolute error loss or l1-norm loss.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LinearRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @Since("1.5.0")
   val meanAbsoluteError: Double = metrics.meanAbsoluteError
@@ -554,6 +560,9 @@ class LinearRegressionSummary private[regression] (
   /**
    * Returns the mean squared error, which is a risk function corresponding to the
    * expected value of the squared error loss or quadratic loss.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LinearRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @Since("1.5.0")
   val meanSquaredError: Double = metrics.meanSquaredError
@@ -561,6 +570,9 @@ class LinearRegressionSummary private[regression] (
   /**
    * Returns the root mean squared error, which is defined as the square root of
    * the mean squared error.
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LinearRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @Since("1.5.0")
   val rootMeanSquaredError: Double = metrics.rootMeanSquaredError
@@ -568,6 +580,9 @@ class LinearRegressionSummary private[regression] (
   /**
    * Returns R^2^, the coefficient of determination.
    * Reference: [[http://en.wikipedia.org/wiki/Coefficient_of_determination]]
+   *
+   * Note: This ignores instance weights (setting all to 1.0) from [[LinearRegression.weightCol]].
+   *       This will change in later Spark versions.
    */
   @Since("1.5.0")
   val r2: Double = metrics.r2