[SPARK-15608][ML][EXAMPLES][DOC] add examples and documents of ml.isotonic regression

## What changes were proposed in this pull request?

add ml doc for ml isotonic regression
add scala example for ml isotonic regression
add java example for ml isotonic regression
add python example for ml isotonic regression

modify scala example for mllib isotonic regression
modify java example for mllib isotonic regression
modify python example for mllib isotonic regression

add data/mllib/sample_isotonic_regression_libsvm_data.txt
delete data/mllib/sample_isotonic_regression_data.txt
## How was this patch tested?

N/A

Author: WeichenXu <WeichenXu123@outlook.com>

Closes #13381 from WeichenXu123/add_isotonic_regression_doc.

1 files changed, 8 insertions, 3 deletions

diff --git a/examples/src/main/python/mllib/isotonic_regression_example.py b/examples/src/main/python/mllib/isotonic_regression_example.py
index 89dc9f4b66..33d618ab48 100644
--- a/examples/src/main/python/mllib/isotonic_regression_example.py
+++ b/examples/src/main/python/mllib/isotonic_regression_example.py
@@ -23,7 +23,8 @@ from __future__ import print_function
 from pyspark import SparkContext
 # $example on$
 import math
-from pyspark.mllib.regression import IsotonicRegression, IsotonicRegressionModel
+from pyspark.mllib.regression import LabeledPoint, IsotonicRegression, IsotonicRegressionModel
+from pyspark.mllib.util import MLUtils
 # $example off$
 
 if __name__ == "__main__":
@@ -31,10 +32,14 @@ if __name__ == "__main__":
     sc = SparkContext(appName="PythonIsotonicRegressionExample")
 
     # $example on$
-    data = sc.textFile("data/mllib/sample_isotonic_regression_data.txt")
+    # Load and parse the data
+    def parsePoint(labeledData):
+        return (labeledData.label, labeledData.features[0], 1.0)
+
+    data = MLUtils.loadLibSVMFile(sc, "data/mllib/sample_isotonic_regression_libsvm_data.txt")
 
     # Create label, feature, weight tuples from input data with weight set to default value 1.0.
-    parsedData = data.map(lambda line: tuple([float(x) for x in line.split(',')]) + (1.0,))
+    parsedData = data.map(parsePoint)
 
     # Split data into training (60%) and test (40%) sets.
     training, test = parsedData.randomSplit([0.6, 0.4], 11)