[SPARK-14339][DOC] Add python examples for DCT,MinMaxScaler,MaxAbsScaler

## What changes were proposed in this pull request?
add three python examples

## How was this patch tested?
manual tests

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #12063 from zhengruifeng/dct_pe.

docs/ml-features.md

@@ -413,6 +413,14 @@ for more details on the API.
 
 {% include_example java/org/apache/spark/examples/ml/JavaDCTExample.java %}
 </div>
+
+<div data-lang="python" markdown="1">
+
+Refer to the [DCT Python docs](api/python/pyspark.ml.html#pyspark.ml.feature.DCT)
+for more details on the API.
+
+{% include_example python/ml/dct_example.py %}
+</div>
 </div>
 
 ## StringIndexer
@@ -771,6 +779,14 @@ for more details on the API.
 
 {% include_example java/org/apache/spark/examples/ml/JavaMinMaxScalerExample.java %}
 </div>
+
+<div data-lang="python" markdown="1">
+
+Refer to the [MinMaxScaler Python docs](api/python/pyspark.ml.html#pyspark.ml.feature.MinMaxScaler)
+for more details on the API.
+
+{% include_example python/ml/min_max_scaler_example.py %}
+</div>
 </div>
 
 
@@ -803,6 +819,14 @@ for more details on the API.
 
 {% include_example java/org/apache/spark/examples/ml/JavaMaxAbsScalerExample.java %}
 </div>
+
+<div data-lang="python" markdown="1">
+
+Refer to the [MaxAbsScaler Python docs](api/python/pyspark.ml.html#pyspark.ml.feature.MaxAbsScaler)
+for more details on the API.
+
+{% include_example python/ml/max_abs_scaler_example.py %}
+</div>
 </div>
 
 ## Bucketizer

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

+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import print_function
+
+from pyspark import SparkContext
+from pyspark.sql import SQLContext
+# $example on$
+from pyspark.ml.feature import DCT
+from pyspark.mllib.linalg import Vectors
+# $example off$
+
+if __name__ == "__main__":
+    sc = SparkContext(appName="DCTExample")
+    sqlContext = SQLContext(sc)
+
+    # $example on$
+    df = sqlContext.createDataFrame([
+        (Vectors.dense([0.0, 1.0, -2.0, 3.0]),),
+        (Vectors.dense([-1.0, 2.0, 4.0, -7.0]),),
+        (Vectors.dense([14.0, -2.0, -5.0, 1.0]),)], ["features"])
+
+    dct = DCT(inverse=False, inputCol="features", outputCol="featuresDCT")
+
+    dctDf = dct.transform(df)
+
+    for dcts in dctDf.select("featuresDCT").take(3):
+        print(dcts)
+    # $example off$
+
+    sc.stop()

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

+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import print_function
+
+from pyspark import SparkContext
+from pyspark.sql import SQLContext
+# $example on$
+from pyspark.ml.feature import MaxAbsScaler
+# $example off$
+
+if __name__ == "__main__":
+    sc = SparkContext(appName="MaxAbsScalerExample")
+    sqlContext = SQLContext(sc)
+
+    # $example on$
+    dataFrame = sqlContext.read.format("libsvm").load("data/mllib/sample_libsvm_data.txt")
+
+    scaler = MaxAbsScaler(inputCol="features", outputCol="scaledFeatures")
+
+    # Compute summary statistics and generate MaxAbsScalerModel
+    scalerModel = scaler.fit(dataFrame)
+
+    # rescale each feature to range [-1, 1].
+    scaledData = scalerModel.transform(dataFrame)
+    scaledData.show()
+    # $example off$
+
+    sc.stop()

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

+#
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from __future__ import print_function
+
+from pyspark import SparkContext
+from pyspark.sql import SQLContext
+# $example on$
+from pyspark.ml.feature import MinMaxScaler
+# $example off$
+
+if __name__ == "__main__":
+    sc = SparkContext(appName="MinMaxScalerExample")
+    sqlContext = SQLContext(sc)
+
+    # $example on$
+    dataFrame = sqlContext.read.format("libsvm").load("data/mllib/sample_libsvm_data.txt")
+
+    scaler = MinMaxScaler(inputCol="features", outputCol="scaledFeatures")
+
+    # Compute summary statistics and generate MinMaxScalerModel
+    scalerModel = scaler.fit(dataFrame)
+
+    # rescale each feature to range [min, max].
+    scaledData = scalerModel.transform(dataFrame)
+    scaledData.show()
+    # $example off$
+
+    sc.stop()