Github user thunterdb commented on a diff in the pull request:

    https://github.com/apache/spark/pull/10207#discussion_r47043656
  
    --- Diff: docs/ml-classification-regression.md ---
    @@ -0,0 +1,762 @@
    +---
    +layout: global
    +title: Classification and regression - spark.ml
    +displayTitle: Classification and regression in spark.ml
    +---
    +
    +
    +`\[
    +\newcommand{\R}{\mathbb{R}}
    +\newcommand{\E}{\mathbb{E}}
    +\newcommand{\x}{\mathbf{x}}
    +\newcommand{\y}{\mathbf{y}}
    +\newcommand{\wv}{\mathbf{w}}
    +\newcommand{\av}{\mathbf{\alpha}}
    +\newcommand{\bv}{\mathbf{b}}
    +\newcommand{\N}{\mathbb{N}}
    +\newcommand{\id}{\mathbf{I}}
    +\newcommand{\ind}{\mathbf{1}}
    +\newcommand{\0}{\mathbf{0}}
    +\newcommand{\unit}{\mathbf{e}}
    +\newcommand{\one}{\mathbf{1}}
    +\newcommand{\zero}{\mathbf{0}}
    +\]`
    +
    +**Table of Contents**
    +
    +* This will become a table of contents (this text will be scraped).
    +{:toc}
    +
    +In MLlib, we implement popular linear methods such as logistic
    +regression and linear least squares with $L_1$ or $L_2$ regularization.
    +Refer to [the linear methods in mllib](mllib-linear-methods.html) for
    +details.  In `spark.ml`, we also include Pipelines API for [Elastic
    +net](http://en.wikipedia.org/wiki/Elastic_net_regularization), a hybrid
    +of $L_1$ and $L_2$ regularization proposed in [Zou et al, Regularization
    +and variable selection via the elastic
    +net](http://users.stat.umn.edu/~zouxx019/Papers/elasticnet.pdf).
    +Mathematically, it is defined as a convex combination of the $L_1$ and
    +the $L_2$ regularization terms:
    +`\[
    +\alpha \left( \lambda \|\wv\|_1 \right) + (1-\alpha) \left( 
\frac{\lambda}{2}\|\wv\|_2^2 \right) , \alpha \in [0, 1], \lambda \geq 0
    +\]`
    +By setting $\alpha$ properly, elastic net contains both $L_1$ and $L_2$
    +regularization as special cases. For example, if a [linear
    +regression](https://en.wikipedia.org/wiki/Linear_regression) model is
    +trained with the elastic net parameter $\alpha$ set to $1$, it is
    +equivalent to a
    +[Lasso](http://en.wikipedia.org/wiki/Least_squares#Lasso_method) model.
    +On the other hand, if $\alpha$ is set to $0$, the trained model reduces
    +to a [ridge
    +regression](http://en.wikipedia.org/wiki/Tikhonov_regularization) model.
    +We implement Pipelines API for both linear regression and logistic
    +regression with elastic net regularization.
    +
    +
    +# Classification
    +
    +## Logistic regression
    +
    +Logistic regression is a popular method to predict a binary response. It 
is a special case of [Generalized Linear 
models](https://en.wikipedia.org/wiki/Generalized_linear_model) that predicts 
the probability of the outcome.
    +For more background and more details about the implementation, refer to 
the documentation of the [logistic regression in 
`spark.mllib`](mllib-linear-methods.html#logistic-regression). 
    +
    +  > The current implementation of logistic regression in `spark.ml` only 
supports binary classes. Support for multiclass regression will be added in the 
future.
    +
    +The following example shows how to train a logistic regression model
    +with elastic net regularization. `elasticNetParam` corresponds to
    +$\alpha$ and `regParam` corresponds to $\lambda$.
    +
    +<div class="codetabs">
    +
    +<div data-lang="scala" markdown="1">
    +{% include_example 
scala/org/apache/spark/examples/ml/LogisticRegressionWithElasticNetExample.scala
 %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +{% include_example 
java/org/apache/spark/examples/ml/JavaLogisticRegressionWithElasticNetExample.java
 %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +{% include_example python/ml/logistic_regression_with_elastic_net.py %}
    +</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 `Dataframe` in
    +`BinaryLogisticRegressionSummary` are annotated `@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:
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/LogisticRegressionSummaryExample.scala %}
    +</div>
    +
    +<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:
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaLogisticRegressionSummaryExample.java %}
    +</div>
    +
    +<!--- TODO: Add python model summaries once implemented -->
    +<div data-lang="python" markdown="1">
    +Logistic regression model summary is not yet supported in Python.
    +</div>
    +
    +</div>
    +
    +
    +## Classification with decision trees
    +
    +Decision trees are a popular family of classification and regression 
methods.
    +More information about the `spark.ml` implementation can be found further 
in the [section on decision trees](#decision-trees).
    +
    +The following examples load a dataset in LibSVM format, split it into 
training and test sets, train on the first dataset, and then evaluate on the 
held-out test set.
    +We use two feature transformers to prepare the data; these help index 
categories for the label and categorical features, adding metadata to the 
`DataFrame` which the Decision Tree algorithm can recognize.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +More details on parameters can be found in the [Scala API 
documentation](api/scala/index.html#org.apache.spark.ml.classification.DecisionTreeClassifier).
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/DecisionTreeClassificationExample.scala %}
    +
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +More details on parameters can be found in the [Java API 
documentation](api/java/org/apache/spark/ml/classification/DecisionTreeClassifier.html).
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaDecisionTreeClassificationExample.java %}
    +
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +More details on parameters can be found in the [Python API 
documentation](api/python/pyspark.ml.html#pyspark.ml.classification.DecisionTreeClassifier).
    +
    +{% include_example python/ml/decision_tree_classification_example.py %}
    +
    +</div>
    +
    +</div>
    +
    +## Classification with random forests
    +
    +Random forests are a popular family of classification and regression 
methods.
    +More information about the `spark.ml` implementation can be found further 
in the [section on random forests](#random-forests).
    +
    +The following examples load a dataset in LibSVM format, split it into 
training and test sets, train on the first dataset, and then evaluate on the 
held-out test set.
    +We use two feature transformers to prepare the data; these help index 
categories for the label and categorical features, adding metadata to the 
`DataFrame` which the tree-based algorithms can recognize.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +Refer to the [Scala API 
docs](api/scala/index.html#org.apache.spark.ml.classification.RandomForestClassifier)
 for more details.
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/RandomForestClassifierExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +Refer to the [Java API 
docs](api/java/org/apache/spark/ml/classification/RandomForestClassifier.html) 
for more details.
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaRandomForestClassifierExample.java %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +Refer to the [Python API 
docs](api/python/pyspark.ml.html#pyspark.ml.classification.RandomForestClassifier)
 for more details.
    +
    +{% include_example python/ml/random_forest_classifier_example.py %}
    +</div>
    +</div>
    +
    +## Classification with gradient-boosted trees
    +
    +Gradient-boosted trees (GBTs) are a popular classification and regression 
method using ensembles of decision trees. 
    +More information about the `spark.ml` implementation can be found further 
in the [section on GBTs](#gradient-boosted-trees-gbts).
    +
    +The following examples load a dataset in LibSVM format, split it into 
training and test sets, train on the first dataset, and then evaluate on the 
held-out test set.
    +We use two feature transformers to prepare the data; these help index 
categories for the label and categorical features, adding metadata to the 
`DataFrame` which the tree-based algorithms can recognize.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +Refer to the [Scala API 
docs](api/scala/index.html#org.apache.spark.ml.classification.GBTClassifier) 
for more details.
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/GradientBoostedTreeClassifierExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +Refer to the [Java API 
docs](api/java/org/apache/spark/ml/classification/GBTClassifier.html) for more 
details.
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaGradientBoostedTreeClassifierExample.java 
%}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +Refer to the [Python API 
docs](api/python/pyspark.ml.html#pyspark.ml.classification.GBTClassifier) for 
more details.
    +
    +{% include_example python/ml/gradient_boosted_tree_classifier_example.py %}
    +</div>
    +</div>
    +
    +## Multilayer perceptron classifier
    +
    +Multilayer perceptron classifier (MLPC) is a classifier based on the 
[feedforward artificial neural 
network](https://en.wikipedia.org/wiki/Feedforward_neural_network). 
    +MLPC consists of multiple layers of nodes. 
    +Each layer is fully connected to the next layer in the network. Nodes in 
the input layer represent the input data. All other nodes maps inputs to the 
outputs 
    +by performing linear combination of the inputs with the node's weights 
`$\wv$` and bias `$\bv$` and applying an activation function. 
    +It can be written in matrix form for MLPC with `$K+1$` layers as follows:
    +`\[
    +\mathrm{y}(\x) = \mathrm{f_K}(...\mathrm{f_2}(\wv_2^T\mathrm{f_1}(\wv_1^T 
\x+b_1)+b_2)...+b_K)
    +\]`
    +Nodes in intermediate layers use sigmoid (logistic) function:
    +`\[
    +\mathrm{f}(z_i) = \frac{1}{1 + e^{-z_i}}
    +\]`
    +Nodes in the output layer use softmax function:
    +`\[
    +\mathrm{f}(z_i) = \frac{e^{z_i}}{\sum_{k=1}^N e^{z_k}}
    +\]`
    +The number of nodes `$N$` in the output layer corresponds to the number of 
classes. 
    +
    +MLPC employes backpropagation for learning the model. We use logistic loss 
function for optimization and L-BFGS as optimization routine.
    +
    +**Examples**
    +
    +<div class="codetabs">
    +
    +<div data-lang="scala" markdown="1">
    +{% include_example 
scala/org/apache/spark/examples/ml/MultilayerPerceptronClassifierExample.scala 
%}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +{% include_example 
java/org/apache/spark/examples/ml/JavaMultilayerPerceptronClassifierExample.java
 %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +{% include_example python/ml/multilayer_perceptron_classification.py %}
    +</div>
    +
    +</div>
    +
    +
    +## One-vs-Rest classifier (a.k.a. One-vs-All)
    +
    
+[OneVsRest](http://en.wikipedia.org/wiki/Multiclass_classification#One-vs.-rest)
 is an example of a machine learning reduction for performing multiclass 
classification given a base classifier that can perform binary classification 
efficiently.  It is also known as "One-vs-All."
    +
    +`OneVsRest` is implemented as an `Estimator`. For the base classifier it 
takes instances of `Classifier` and creates a binary classification problem for 
each of the k classes. The classifier for class i is trained to predict whether 
the label is i or not, distinguishing class i from all other classes.
    +
    +Predictions are done by evaluating each binary classifier and the index of 
the most confident classifier is output as label.
    +
    +### Example
    +
    +The example below demonstrates how to load the
    +[Iris 
dataset](http://www.csie.ntu.edu.tw/~cjlin/libsvmtools/datasets/multiclass/iris.scale),
 parse it as a DataFrame and perform multiclass classification using 
`OneVsRest`. The test error is calculated to measure the algorithm accuracy.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +Refer to the [Scala API 
docs](api/scala/index.html#org.apache.spark.ml.classifier.OneVsRest) for more 
details.
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/OneVsRestExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +Refer to the [Java API 
docs](api/java/org/apache/spark/ml/classification/OneVsRest.html) for more 
details.
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaOneVsRestExample.java %}
    +</div>
    +</div>
    +
    +
    +# Regression
    +
    +## Linear regression
    +
    +The interface for working with linear regression models and model
    +summaries is similar to the logistic regression case. The following
    +example demonstrates training an elastic net regularized linear
    +regression model and extracting model summary statistics.
    +
    +<div class="codetabs">
    +
    +<div data-lang="scala" markdown="1">
    +{% include_example 
scala/org/apache/spark/examples/ml/LinearRegressionWithElasticNetExample.scala 
%}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +{% include_example 
java/org/apache/spark/examples/ml/JavaLinearRegressionWithElasticNetExample.java
 %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +<!--- TODO: Add python model summaries once implemented -->
    +{% include_example python/ml/linear_regression_with_elastic_net.py %}
    +</div>
    +
    +</div>
    +
    +
    +## Regression with decision trees
    +
    +Decision trees are a popular family of classification and regression 
methods.
    +More information about the `spark.ml` implementation can be found further 
in the [section on decision trees](#decision-trees).
    +
    +The following examples load a dataset in LibSVM format, split it into 
training and test sets, train on the first dataset, and then evaluate on the 
held-out test set.
    +We use a feature transformer to index categorical features, adding 
metadata to the `DataFrame` which the Decision Tree algorithm can recognize.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +More details on parameters can be found in the [Scala API 
documentation](api/scala/index.html#org.apache.spark.ml.regression.DecisionTreeRegressor).
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/DecisionTreeRegressionExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +More details on parameters can be found in the [Java API 
documentation](api/java/org/apache/spark/ml/regression/DecisionTreeRegressor.html).
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaDecisionTreeRegressionExample.java %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +More details on parameters can be found in the [Python API 
documentation](api/python/pyspark.ml.html#pyspark.ml.regression.DecisionTreeRegressor).
    +
    +{% include_example python/ml/decision_tree_regression_example.py %}
    +</div>
    +
    +</div>
    +
    +
    +## Regression with random forests
    +
    +Random forests are a popular family of classification and regression 
methods.
    +More information about the `spark.ml` implementation can be found further 
in the [section on random forests](#random-forests).
    +
    +The following examples load a dataset in LibSVM format, split it into 
training and test sets, train on the first dataset, and then evaluate on the 
held-out test set.
    +We use a feature transformer to index categorical features, adding 
metadata to the `DataFrame` which the tree-based algorithms can recognize.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +Refer to the [Scala API 
docs](api/scala/index.html#org.apache.spark.ml.regression.RandomForestRegressor)
 for more details.
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/RandomForestRegressorExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +Refer to the [Java API 
docs](api/java/org/apache/spark/ml/regression/RandomForestRegressor.html) for 
more details.
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaRandomForestRegressorExample.java %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +Refer to the [Python API 
docs](api/python/pyspark.ml.html#pyspark.ml.regression.RandomForestRegressor) 
for more details.
    +
    +{% include_example python/ml/random_forest_regressor_example.py %}
    +</div>
    +</div>
    +
    +## Regression with gradient-boosted trees
    +
    +Gradient-boosted trees (GBTs) are a popular regression method using 
ensembles of decision trees. 
    +More information about the `spark.ml` implementation can be found further 
in the [section on GBTs](#gradient-boosted-trees-gbts).
    +
    +Note: For this example dataset, `GBTRegressor` actually only needs 1 
iteration, but that will not
    +be true in general.
    +
    +<div class="codetabs">
    +<div data-lang="scala" markdown="1">
    +
    +Refer to the [Scala API 
docs](api/scala/index.html#org.apache.spark.ml.regression.GBTRegressor) for 
more details.
    +
    +{% include_example 
scala/org/apache/spark/examples/ml/GradientBoostedTreeRegressorExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +
    +Refer to the [Java API 
docs](api/java/org/apache/spark/ml/regression/GBTRegressor.html) for more 
details.
    +
    +{% include_example 
java/org/apache/spark/examples/ml/JavaGradientBoostedTreeRegressorExample.java 
%}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +
    +Refer to the [Python API 
docs](api/python/pyspark.ml.html#pyspark.ml.regression.GBTRegressor) for more 
details.
    +
    +{% include_example python/ml/gradient_boosted_tree_regressor_example.py %}
    +</div>
    +</div>
    +
    +
    +## Survival regression
    +
    +
    +In `spark.ml`, we implement the [Accelerated failure time 
(AFT)](https://en.wikipedia.org/wiki/Accelerated_failure_time_model) 
    +model which is a parametric survival regression model for censored data. 
    +It describes a model for the log of survival time, so it's often called 
    +log-linear model for survival analysis. Different from 
    +[Proportional 
hazards](https://en.wikipedia.org/wiki/Proportional_hazards_model) model
    +designed for the same purpose, the AFT model is more easily to parallelize 
    +because each instance contribute to the objective function independently.
    +
    +Given the values of the covariates $x^{'}$, for random lifetime $t_{i}$ of 
    +subjects i = 1, ..., n, with possible right-censoring, 
    +the likelihood function under the AFT model is given as:
    +`\[
    
+L(\beta,\sigma)=\prod_{i=1}^n[\frac{1}{\sigma}f_{0}(\frac{\log{t_{i}}-x^{'}\beta}{\sigma})]^{\delta_{i}}S_{0}(\frac{\log{t_{i}}-x^{'}\beta}{\sigma})^{1-\delta_{i}}
    +\]`
    +Where $\delta_{i}$ is the indicator of the event has occurred i.e. 
uncensored or not.
    +Using $\epsilon_{i}=\frac{\log{t_{i}}-x^{'}\beta}{\sigma}$, the 
log-likelihood function
    +assumes the form:
    +`\[
    
+\iota(\beta,\sigma)=\sum_{i=1}^{n}[-\delta_{i}\log\sigma+\delta_{i}\log{f_{0}}(\epsilon_{i})+(1-\delta_{i})\log{S_{0}(\epsilon_{i})}]
    +\]`
    +Where $S_{0}(\epsilon_{i})$ is the baseline survivor function,
    +and $f_{0}(\epsilon_{i})$ is corresponding density function.
    +
    +The most commonly used AFT model is based on the Weibull distribution of 
the survival time. 
    +The Weibull distribution for lifetime corresponding to extreme value 
distribution for 
    +log of the lifetime, and the $S_{0}(\epsilon)$ function is:
    +`\[   
    +S_{0}(\epsilon_{i})=\exp(-e^{\epsilon_{i}})
    +\]`
    +the $f_{0}(\epsilon_{i})$ function is:
    +`\[
    +f_{0}(\epsilon_{i})=e^{\epsilon_{i}}\exp(-e^{\epsilon_{i}})
    +\]`
    +The log-likelihood function for AFT model with Weibull distribution of 
lifetime is:
    +`\[
    +\iota(\beta,\sigma)= 
-\sum_{i=1}^n[\delta_{i}\log\sigma-\delta_{i}\epsilon_{i}+e^{\epsilon_{i}}]
    +\]`
    +Due to minimizing the negative log-likelihood equivalent to maximum a 
posteriori probability,
    +the loss function we use to optimize is $-\iota(\beta,\sigma)$.
    +The gradient functions for $\beta$ and $\log\sigma$ respectively are:
    +`\[   
    +\frac{\partial (-\iota)}{\partial 
\beta}=\sum_{1=1}^{n}[\delta_{i}-e^{\epsilon_{i}}]\frac{x_{i}}{\sigma}
    +\]`
    +`\[ 
    +\frac{\partial (-\iota)}{\partial 
(\log\sigma)}=\sum_{i=1}^{n}[\delta_{i}+(\delta_{i}-e^{\epsilon_{i}})\epsilon_{i}]
    +\]`
    +
    +The AFT model can be formulated as a convex optimization problem, 
    +i.e. the task of finding a minimizer of a convex function 
$-\iota(\beta,\sigma)$ 
    +that depends coefficients vector $\beta$ and the log of scale parameter 
$\log\sigma$.
    +The optimization algorithm underlying the implementation is L-BFGS.
    +The implementation matches the result from R's survival function 
    
+[survreg](https://stat.ethz.ch/R-manual/R-devel/library/survival/html/survreg.html)
    +
    +### Survival regression example
    +
    +<div class="codetabs">
    +
    +<div data-lang="scala" markdown="1">
    +{% include_example 
scala/org/apache/spark/examples/ml/AFTSurvivalRegressionExample.scala %}
    +</div>
    +
    +<div data-lang="java" markdown="1">
    +{% include_example 
java/org/apache/spark/examples/ml/JavaAFTSurvivalRegressionExample.java %}
    +</div>
    +
    +<div data-lang="python" markdown="1">
    +{% include_example python/ml/aft_survival_regression.py %}
    +</div>
    +
    +</div>
    +
    +
    +
    +# Decision trees
    +
    +[Decision trees](http://en.wikipedia.org/wiki/Decision_tree_learning)
    +and their ensembles are popular methods for the machine learning tasks of
    +classification and regression. Decision trees are widely used since they 
are easy to interpret,
    +handle categorical features, extend to the multiclass classification 
setting, do not require
    +feature scaling, and are able to capture non-linearities and feature 
interactions. Tree ensemble
    +algorithms such as random forests and boosting are among the top 
performers for classification and
    +regression tasks.
    +
    +MLlib supports decision trees for binary and multiclass classification and 
for regression,
    +using both continuous and categorical features. The implementation 
partitions data by rows,
    +allowing distributed training with millions or even billions of instances.
    +
    +Users can find more information about the decision tree algorithm in the 
[MLlib Decision Tree guide](mllib-decision-tree.html).  In this section, we 
demonstrate the Pipelines API for Decision Trees.
    +
    +The Pipelines API for Decision Trees offers a bit more functionality than 
the original API.  In particular, for classification, users can get the 
predicted probability of each class (a.k.a. class conditional probabilities).
    +
    +Ensembles of trees (Random Forests and Gradient-Boosted Trees) are 
described in the [Ensembles guide](ml-ensembles.html).
    +
    +## Inputs and Outputs
    +
    +We list the input and output (prediction) column types here.
    +All output columns are optional; to exclude an output column, set its 
corresponding Param to an empty string.
    +
    +### Input Columns
    +
    +<table class="table">
    +  <thead>
    +    <tr>
    +      <th align="left">Param name</th>
    +      <th align="left">Type(s)</th>
    +      <th align="left">Default</th>
    +      <th align="left">Description</th>
    +    </tr>
    +  </thead>
    +  <tbody>
    +    <tr>
    +      <td>labelCol</td>
    +      <td>Double</td>
    +      <td>"label"</td>
    +      <td>Label to predict</td>
    +    </tr>
    +    <tr>
    +      <td>featuresCol</td>
    +      <td>Vector</td>
    +      <td>"features"</td>
    +      <td>Feature vector</td>
    +    </tr>
    +  </tbody>
    +</table>
    +
    +### Output Columns
    +
    +<table class="table">
    +  <thead>
    +    <tr>
    +      <th align="left">Param name</th>
    +      <th align="left">Type(s)</th>
    +      <th align="left">Default</th>
    +      <th align="left">Description</th>
    +      <th align="left">Notes</th>
    +    </tr>
    +  </thead>
    +  <tbody>
    +    <tr>
    +      <td>predictionCol</td>
    +      <td>Double</td>
    +      <td>"prediction"</td>
    +      <td>Predicted label</td>
    +      <td></td>
    +    </tr>
    +    <tr>
    +      <td>rawPredictionCol</td>
    +      <td>Vector</td>
    +      <td>"rawPrediction"</td>
    +      <td>Vector of length # classes, with the counts of training instance 
labels at the tree node which makes the prediction</td>
    +      <td>Classification only</td>
    +    </tr>
    +    <tr>
    +      <td>probabilityCol</td>
    +      <td>Vector</td>
    +      <td>"probability"</td>
    +      <td>Vector of length # classes equal to rawPrediction normalized to 
a multinomial distribution</td>
    +      <td>Classification only</td>
    +    </tr>
    +  </tbody>
    +</table>
    +
    +## Examples
    +
    +The below examples demonstrate the Pipelines API for Decision Trees. The 
main differences between this API and the [original MLlib Decision Tree 
API](mllib-decision-tree.html) are:
    --- End diff --
    
    Yes, I missed this paragraph during the copy/paste. I removed this section 
and moved the explanations about the differences to the main section (`# 
Ensembles`, ...)


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