fix indentions

Author: yinxusen

docs/_plugins/include_example.rb

@@ -24,20 +24,54 @@ def render(context)
       Pygments.highlight(code, :lexer => @lang)
     end
 
-    # Select lines according to labels in code. Currently we use "begin code" and "end code" as
-    # labels.
+    # Trim the code block so as to have the same indention, regardless of their positions in the
+    # code file.
+    def trim_codeblock(lines)
+      # Select the minimum indention of the current code block.
+      min_start_spaces = lines
+        .select{ |l| l.strip.size !=0 }
+        .map{ |l| l[/\A */].size }
+        .min
+
+      lines.map{ |l| l[min_start_spaces .. -1] }
+    end
+
+    # Select lines according to labels in code. Currently we use "$example on$" and "$example off$"
+    # as labels. Note that code blocks identified by the labels should not overlap.
     def select_lines(code)
       lines = code.each_line.to_a
-      start = lines.each_with_index.select { |l, i| l.include? "$example on$" }.last.last
-      endline = lines.each_with_index.select { |l, i| l.include? "$example off$" }.last.last
-      length = lines.count
- 
-      if start > 0 or endline < length - 1
-        raise "Wrong positions of begin and end tags." if start > endline
-        range = Range.new(start, endline)
-        code = lines[range].join
+
+      # Select the array of start labels from code.
+      startIndices = lines
+        .each_with_index
+        .select{ |l, i| l.include? "$example on$" }
+        .map{ |l, i| i }
+
+      # Select the array of end labels from code.
+      endIndices = lines
+        .each_with_index
+        .select{ |l, i| l.include? "$example off$" }
+        .map{ |l, i| i }
+
+      raise "Start indices amount is not equal to end indices amount, please check the code." \
+        unless startIndices.size == endIndices.size
+
+      raise "No code is selected by include_example, please check the code." \
+        if startIndices.size == 0
+
+      # Select and join code blocks together, with a space line between each of two continuous
+      # blocks.
+      lastIndex = -1
+      result = ""
+      startIndices.zip(endIndices).each do |start, endline|
+        raise "Overlapping between two example code blocks are not allowed." if start <= lastIndex
+        raise "$example on$ should not be in the same line with $example off$." if start == endline
+        lastIndex = endline
+        range = Range.new(start + 1, endline - 1)
+        result += trim_codeblock(lines[range]).join
+        result += "\n"
       end
-      code
+      result
     end
   end
 end

examples/src/main/java/org/apache/spark/examples/ml/JavaCrossValidatorExample.java

@@ -17,6 +17,7 @@
 
 package org.apache.spark.examples.ml;
 
+// $example on$
 import java.util.List;
 
 import com.google.common.collect.Lists;
@@ -36,6 +37,7 @@
 import org.apache.spark.sql.DataFrame;
 import org.apache.spark.sql.Row;
 import org.apache.spark.sql.SQLContext;
+// $example off$
 
 /**
  * A simple example demonstrating model selection using CrossValidator.

examples/src/main/python/ml/cross_validator.py

@@ -17,13 +17,15 @@
 
 from __future__ import print_function
 
+# $example on$
 from pyspark import SparkContext
 from pyspark.ml import Pipeline
 from pyspark.ml.classification import LogisticRegression
 from pyspark.ml.evaluation import BinaryClassificationEvaluator
 from pyspark.ml.feature import HashingTF, Tokenizer
 from pyspark.ml.tuning import CrossValidator, ParamGridBuilder
 from pyspark.sql import Row, SQLContext
+# $example off$
 
 """
 A simple example demonstrating model selection using CrossValidator.

examples/src/main/scala/org/apache/spark/examples/ml/CrossValidatorExample.scala

@@ -18,6 +18,7 @@
 // scalastyle:off println
 package org.apache.spark.examples.ml
 
+// $example on$
 import org.apache.spark.{SparkConf, SparkContext}
 import org.apache.spark.ml.Pipeline
 import org.apache.spark.ml.classification.LogisticRegression
@@ -26,6 +27,7 @@ import org.apache.spark.ml.feature.{HashingTF, Tokenizer}
 import org.apache.spark.ml.tuning.{ParamGridBuilder, CrossValidator}
 import org.apache.spark.mllib.linalg.Vector
 import org.apache.spark.sql.{Row, SQLContext}
+// $example off$
 
 /**
  * A simple example demonstrating model selection using CrossValidator.