[SPARK-15150][EXAMPLE][DOC] Update LDA examples

## What changes were proposed in this pull request?
1,create a libsvm-type dataset for lda: `data/mllib/sample_lda_libsvm_data.txt`
2,add python example
3,directly read the datafile in examples
4,BTW, change to `SparkSession` in `aft_survival_regression.py`

## How was this patch tested?
manual tests
`./bin/spark-submit examples/src/main/python/ml/lda_example.py`

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #12927 from zhengruifeng/lda_pe.

1 files changed, 13 insertions, 6 deletions

diff --git a/examples/src/main/python/ml/aft_survival_regression.py b/examples/src/main/python/ml/aft_survival_regression.py
index 0ee01fd825..9879679829 100644
--- a/examples/src/main/python/ml/aft_survival_regression.py
+++ b/examples/src/main/python/ml/aft_survival_regression.py
@@ -17,19 +17,26 @@
 
 from __future__ import print_function
 
-from pyspark import SparkContext
-from pyspark.sql import SQLContext
 # $example on$
 from pyspark.ml.regression import AFTSurvivalRegression
 from pyspark.mllib.linalg import Vectors
 # $example off$
+from pyspark.sql import SparkSession
+
+"""
+An example demonstrating aft survival regression.
+Run with:
+  bin/spark-submit examples/src/main/python/ml/aft_survival_regression.py
+"""
 
 if __name__ == "__main__":
-    sc = SparkContext(appName="AFTSurvivalRegressionExample")
-    sqlContext = SQLContext(sc)
+    spark = SparkSession \
+        .builder \
+        .appName("PythonAFTSurvivalRegressionExample") \
+        .getOrCreate()
 
     # $example on$
-    training = sqlContext.createDataFrame([
+    training = spark.createDataFrame([
         (1.218, 1.0, Vectors.dense(1.560, -0.605)),
         (2.949, 0.0, Vectors.dense(0.346, 2.158)),
         (3.627, 0.0, Vectors.dense(1.380, 0.231)),
@@ -48,4 +55,4 @@ if __name__ == "__main__":
     model.transform(training).show(truncate=False)
     # $example off$
 
-    sc.stop()
+    spark.stop()