[SPARK-11835] Adds a sidebar menu to MLlib's documentation

This PR adds a sidebar menu when browsing the user guide of MLlib. It uses a YAML file to describe the structure of the documentation. It should be trivial to adapt this to the other projects.

![screen shot 2015-11-18 at 4 46 12 pm](https://cloud.githubusercontent.com/assets/7594753/11259591/a55173f4-8e17-11e5-9340-0aed79d66262.png)

Author: Timothy Hunter <timhunter@databricks.com>

Closes #9826 from thunterdb/spark-11835.

6 files changed, 163 insertions, 8 deletions

diff --git a/docs/_data/menu-ml.yaml b/docs/_data/menu-ml.yaml
new file mode 100644
index 0000000000..dff3d33bf4
--- /dev/null
+++ b/docs/_data/menu-ml.yaml
@@ -0,0 +1,10 @@
+- text: Feature extraction, transformation, and selection
+  url: ml-features.html
+- text: Decision trees for classification and regression
+  url: ml-decision-tree.html
+- text: Ensembles
+  url: ml-ensembles.html
+- text: Linear methods with elastic-net regularization
+  url: ml-linear-methods.html
+- text: Multilayer perceptron classifier
+  url: ml-ann.html
diff --git a/docs/_data/menu-mllib.yaml b/docs/_data/menu-mllib.yaml
new file mode 100644
index 0000000000..12d22abd52
--- /dev/null
+++ b/docs/_data/menu-mllib.yaml
@@ -0,0 +1,75 @@
+- text: Data types
+  url: mllib-data-types.html
+- text: Basic statistics
+  url: mllib-statistics.html
+  subitems:
+    - text: Summary statistics
+      url: mllib-statistics.html#summary-statistics
+    - text: Correlations
+      url: mllib-statistics.html#correlations
+    - text: Stratified sampling
+      url: mllib-statistics.html#stratified-sampling
+    - text: Hypothesis testing
+      url: mllib-statistics.html#hypothesis-testing
+    - text: Random data generation
+      url: mllib-statistics.html#random-data-generation
+- text: Classification and regression
+  url: mllib-classification-regression.html
+  subitems:
+    - text: Linear models (SVMs, logistic regression, linear regression)
+      url: mllib-linear-methods.html
+    - text: Naive Bayes
+      url: mllib-naive-bayes.html
+    - text: decision trees
+      url: mllib-decision-tree.html
+    - text: ensembles of trees (Random Forests and Gradient-Boosted Trees)
+      url: mllib-ensembles.html
+    - text: isotonic regression
+      url: mllib-isotonic-regression.html
+- text: Collaborative filtering
+  url: mllib-collaborative-filtering.html
+  subitems:
+    - text: alternating least squares (ALS)
+      url: mllib-collaborative-filtering.html#collaborative-filtering
+- text: Clustering
+  url: mllib-clustering.html
+  subitems:
+    - text: k-means
+      url: mllib-clustering.html#k-means
+    - text: Gaussian mixture
+      url: mllib-clustering.html#gaussian-mixture
+    - text: power iteration clustering (PIC)
+      url: mllib-clustering.html#power-iteration-clustering-pic
+    - text: latent Dirichlet allocation (LDA)
+      url: mllib-clustering.html#latent-dirichlet-allocation-lda
+    - text: streaming k-means
+      url: mllib-clustering.html#streaming-k-means
+- text: Dimensionality reduction
+  url: mllib-dimensionality-reduction.html
+  subitems:
+    - text: singular value decomposition (SVD)
+      url: mllib-dimensionality-reduction.html#singular-value-decomposition-svd
+    - text: principal component analysis (PCA)
+      url: mllib-dimensionality-reduction.html#principal-component-analysis-pca
+- text: Feature extraction and transformation
+  url: mllib-feature-extraction.html
+- text: Frequent pattern mining
+  url: mllib-frequent-pattern-mining.html
+  subitems:
+    - text: FP-growth
+      url: mllib-frequent-pattern-mining.html#fp-growth
+    - text: association rules
+      url: mllib-frequent-pattern-mining.html#association-rules
+    - text: PrefixSpan
+      url: mllib-frequent-pattern-mining.html#prefix-span
+- text: Evaluation metrics
+  url: mllib-evaluation-metrics.html
+- text: PMML model export
+  url: mllib-pmml-model-export.html
+- text: Optimization (developer)
+  url: mllib-optimization.html
+  subitems:
+    - text: stochastic gradient descent
+      url: mllib-optimization.html#stochastic-gradient-descent-sgd
+    - text: limited-memory BFGS (L-BFGS)
+      url: mllib-optimization.html#limited-memory-bfgs-l-bfgs
diff --git a/docs/_includes/nav-left-wrapper-ml.html b/docs/_includes/nav-left-wrapper-ml.html
new file mode 100644
index 0000000000..0103e890cc
--- /dev/null
+++ b/docs/_includes/nav-left-wrapper-ml.html
@@ -0,0 +1,8 @@
+<div class="left-menu-wrapper">
+    <div class="left-menu">
+        <h3>spark.ml package</h3>
+        {% include nav-left.html nav=include.nav-ml %}
+        <h3>spark.mllib package</h3>
+        {% include nav-left.html nav=include.nav-mllib %}
+    </div>
+</div>
\ No newline at end of file
diff --git a/docs/_includes/nav-left.html b/docs/_includes/nav-left.html
new file mode 100644
index 0000000000..73176f4132
--- /dev/null
+++ b/docs/_includes/nav-left.html
@@ -0,0 +1,17 @@
+{% assign navurl = page.url | remove: 'index.html' %}
+<ul>
+{% for item in include.nav %}
+    <li>
+        <a href="{{ item.url }}">
+            {% if navurl contains item.url %}
+                <b>{{ item.text }}</b>
+            {% else %}
+                {{ item.text }}
+            {% endif %}
+        </a>
+    </li>
+    {% if item.subitems and navurl contains item.url %}
+        {% include nav-left.html nav=item.subitems %}
+    {% endif %}
+{% endfor %}
+</ul>
diff --git a/docs/_layouts/global.html b/docs/_layouts/global.html
index 467ff7a03f..1b09e2221e 100755
--- a/docs/_layouts/global.html
+++ b/docs/_layouts/global.html
@@ -124,16 +124,24 @@
             </div>
         </div>
 
-        <div class="container" id="content">
-          {% if page.displayTitle %}
-            <h1 class="title">{{ page.displayTitle }}</h1>
-          {% else %}
-            <h1 class="title">{{ page.title }}</h1>
-          {% endif %}
+        <div class="container-wrapper">
 
-          {{ content }}
+            {% if page.url contains "/ml" %}
+              {% include nav-left-wrapper-ml.html nav-mllib=site.data.menu-mllib nav-ml=site.data.menu-ml %}
+            {% endif %}
 
-        </div> <!-- /container -->
+
+            <div class="container" id="content">
+              {% if page.displayTitle %}
+                <h1 class="title">{{ page.displayTitle }}</h1>
+              {% else %}
+                <h1 class="title">{{ page.title }}</h1>
+              {% endif %}
+
+              {{ content }}
+
+            </div> <!-- /container -->
+        </div>
 
         <script src="js/vendor/jquery-1.8.0.min.js"></script>
         <script src="js/vendor/bootstrap.min.js"></script>
diff --git a/docs/css/main.css b/docs/css/main.css
index d770173be1..356b324d63 100755
--- a/docs/css/main.css
+++ b/docs/css/main.css
@@ -39,8 +39,18 @@
   margin-left: 10px;
 }
 
+body .container-wrapper {
+  position: absolute;
+  width: 100%;
+  display: flex;
+}
+
 body #content {
+  position: relative;
+
   line-height: 1.6; /* Inspired by Github's wiki style */
+  background-color: white;
+  padding-left: 15px;
 }
 
 .title {
@@ -155,3 +165,30 @@ ul.nav li.dropdown ul.dropdown-menu li.dropdown-submenu ul.dropdown-menu {
  * AnchorJS (anchor links when hovering over headers)
  */
 a.anchorjs-link:hover { text-decoration: none; }
+
+
+/**
+ * The left navigation bar.
+ */
+.left-menu-wrapper {
+  position: absolute;
+  height: 100%;
+
+  width: 256px;
+  margin-top: -20px;
+  padding-top: 20px;
+  background-color: #F0F8FC;
+}
+
+.left-menu {
+  position: fixed;
+  max-width: 350px;
+
+  padding-right: 10px;
+  width: 256px;
+}
+
+.left-menu h3 {
+  margin-left: 10px;
+  line-height: 30px;
+}
\ No newline at end of file