AI與大數據數據處理 Spark實戰(20171216)

Practical Machine Learning in
Spark
Chih-Chieh Hung
Tamkang University

Chih-Chieh Hung 洪智傑
• Tamkang University (Assistant Professor)
2016-
• Rakuten Inc., Japan (Data Scientist)
2013-2015
• Yahoo! Inc., Taiwan (Research Engineer)
2011-2013
• Microsoft Research Asia, China (Research Intern)
2010

Big Data Definition
• No single standard definition…
“Big Data” is data whose scale, diversity, and complexity require new
architecture, techniques, algorithms, and analytics to manage it and
extract value and hidden knowledge from it…
6

Scale (Volume)
• Data Volume
• 44x increase from 2009 to 2020
• From 0.8 zettabytes to 35zb
• Data volume is increasing exponentially

Complexity (Varity)
• Various formats, types, and structures
• Text, numerical, images, audio, video, sequences, time series, social
media data, multi-dim arrays, etc…
• Static data vs. streaming data
• A single application can be generating/collecting many types of data
8
To extract knowledge all these types of
data need to linked together

Speed (Velocity)
• Data is begin generated fast and need to be processed fast
• Online Data Analytics
• Late decisions  missing opportunities

Four V Challenges in Big Data
*. http://www-05.ibm.com/fr/events/netezzaDM_2012/Solutions_Big_Data.pdf

Apache Hadoop
• The Apache™ Hadoop® project develops
open-source software for reliable,
scalable, distributed computing.
• Three major modules:
• Hadoop Distributed File System (HDFS™): A
distributed file system that provides high-
throughput access to application data.
• Hadoop YARN: A framework for job
scheduling and cluster resource
management.
• Hadoop MapReduce: A YARN-based system
for parallel processing of large data sets.

Hadoop Components: HDFS
• File system
• Sit on top of a native file system
• Based on Google’s GFS
• Provide redundant storage
• Read/Write
• Good at large, sequential reads
• Files are “Write once”
• Components
• DataNodes: metadata of files
• NameNodes: actual blocks
• Secondary NameNode: merges the fsimage
and the edits log files periodically and keeps
edits log size within a limit

Hadoop Components: YARN
• Manage resource (Data operating system).
• YARN = Yet Another Resource Negotiator
• Manage and monitor workloads
• Maintain a multi-tenant platform.
• Implement security control.
• Support multiple processing models in addition to MapReduce.

Hadoop Components: MapReduce
• Process data in cluster.
• Two phases: Map + Reduce
• Between the two is the “shuffle-and-sort” stage
• Map
• Operates on a discrete portion of the overall dataset
• Reduce
• After all maps are complete, the intermediate data are separated to nodes
which perform the Reduce phase.

MapReduce Algorithm For Word Count
• Input and Output

Step 1: Design Mapper (Must Implement)
• Write the mapper: output the key-value pair <word, 1>

Step 2: Sort and Shuffle (Don’t Need to Do)
• The values with the same key will send to the same reducer.

Step 3: Design Reducer (Must Implement)
• Write reducer as: (word, sum of all the values)

What is Spark?
Efficient
• General execution graphs
• In-memory storage
Usable
• Rich APIs in Java, Scala, Python
• Interactive shell
• Fast and Expressive Cluster Computing System Compatible
with Apache Hadoop

Key Concepts
Resilient Distributed Datasets
• Collections of objects spread across a
cluster, stored in RAM or on Disk
• Built through parallel transformations
• Automatically rebuilt on failure
Operations
• Transformations
(e.g. map, filter,
groupBy)
• Actions
(e.g. count, collect, save)
• Write programs in terms of transformations on distributed
datasets

Language Support
Standalone Programs
•Python, Scala, & Java
Interactive Shells
• Python & Scala
Performance
• Java & Scala are faster due to
static typing
• …but Python is often fine
Python
lines = sc.textFile(...)
lines.filter(lambda s: “ERROR” in s).count()
Scala
val lines = sc.textFile(...)
lines.filter(x => x.contains(“ERROR”)).count()
Java
JavaRDD<String> lines = sc.textFile(...);
lines.filter(new Function<String, Boolean>() {
Boolean call(String s) {
return s.contains(“error”);
}
}).count();

import sys
from pyspark import SparkContext
if __name__ == "__main__":
sc = SparkContext( “local”, “WordCount”, sys.argv[0], None)
lines = sc.textFile(sys.argv[1])
counts = lines.flatMap(lambda s: s.split(“ ”))
.map(lambda word: (word, 1))
.reduceByKey(lambda x, y: x + y)
counts.saveAsTextFile(sys.argv[2])
An Simple Example of Spark App
sc
RDD
ops

SparkContext
• Main entry point
• SparkContext is the object that manages the connection to the clusters in Spark
and coordinates running processes on the clusters themselves. SparkContext
connects to cluster managers, which manage the actual executors that run the
specific computations

SparkContext
• Main entry point to Spark functionality
• Available in shell as variable sc
• In standalone programs, you’d make your own (see later for details)

Create SparkContext: Local Mode
• Very simple

Create SparkContext: Cluster Mode
• Need to write SparkConf about the clusters

Resilient Distributed Datasets (RDD)
• An RDD is Spark's representation of a dataset that is distributed
across the RAM, or memory, of lots of machines.
• An RDD object is essentially a collection of elements that you can use
to hold lists of tuples, dictionaries, lists, etc.
• Lazy Evaluation : the ability to lazily evaluate code, postponing
running a calculation until absolutely necessary.
•

Transformation and Actions in Spark
• RDDs have actions, which return values, and transformations, which
return pointers to new RDDs.
• RDDs’ value is only updated once that RDD is computed as part of an
action

Example: Log Mining
Load error messages from a log into memory, then interactively search
for various patterns
lines = spark.textFile(“hdfs://...”)
errors = lines.filter(lambda s: s.startswith(“ERROR”))
messages = errors.map(lambda s: s.split(“t”)[2])
messages.cache()
Block 1
Block 2
Block 3
Worker
Worker
Worker
Driver
messages.filter(lambda s: “mysql” in s).count()
messages.filter(lambda s: “php” in s).count()
. . .
tasks
results
Cache 1
Cache 2
Cache 3
Base RDDTransformed RDD
Action
Full-text search of Wikipedia
• 60GB on 20 EC2 machine
• 0.5 sec vs. 20s for on-disk

Creating RDDs
# Turn a Python collection into an RDD
>sc.parallelize([1, 2, 3])
# Load text file from local FS, HDFS, or S3
>sc.textFile(“file.txt”)
>sc.textFile(“directory/*.txt”)
>sc.textFile(“hdfs://namenode:9000/path/file”)
# Use existing Hadoop InputFormat (Java/Scala only)
>sc.hadoopFile(keyClass, valClass, inputFmt, conf)

Most Widely-Used Action and Transformation

Basic Transformations
>nums = sc.parallelize([1, 2, 3])
# Pass each element through a function
>squares = nums.map(lambda x: x*x) // {1, 4, 9}
# Keep elements passing a predicate
>even = squares.filter(lambda x: x % 2 == 0) // {4}
# Map each element to zero or more others
>nums.flatMap(lambda x: => range(x))
> # => {0, 0, 1, 0, 1, 2}
Range object (sequence
of numbers 0, 1, …, x-1)

map() and flatMap()
• map()
map() transformation applies changes on each line of the RDD and
returns the transformed RDD as iterable of iterables i.e. each line is
equivalent to a iterable and the entire RDD is itself a list

map() and flatMap()
• flatMap()
This transformation apply changes to each line same as map but the
return is not a iterable of iterables but it is only an iterable holding
entire RDD contents.

map() and flatMap() examples
>lines.take(2)
[‘#good d#ay #’,
‘#good #weather’]
>words = lines.map(lambda lines: lines.split(' '))
[[‘#good’, ‘d#ay’, ’#’],
[‘#good’, ‘#weather’]]
>words = lines. flatMap(lambda lines: lines.split('
'))
[‘#good’, ‘d#ay’, ‘#’, ‘#good’, ‘#weather’]

Filter()
• Filter() transformation is used to reduce the old RDD based on some
condition.

Filter() example
• How to filter out hashtags from words
>hashtags = words.filter(lambda word:
word.startswith("#")).filter(lambda word: word !=
"#")
[‘#good’, ‘#good’, ‘#weather’]

Join()
• Return a RDD containing all pairs of elements having the same key in
the original RDDs

KeyBy()
• Create a Pair RDD, forming one pair for each item in the original RDD.
The pair’s key is calculated from the value via a user-defined function.

GroupBy()
• Group the data in the original RDD. Create pairs where the key is the
output of a user function, and the value is all items for which the
function yields this key.

GroupByKey()
• Group the values for each key in the original RDD. Create a new pair
where the original key corresponds to this collected group of values.

ReduceByKey()
• reduceByKey(f) combines tuples with the same key using the function
we specify f.
>hashtagsNum = hashtags.map(lambda word: (word, 1))
[(‘#good’,1), (‘#good’, 1), (‘#weather’, 1)]
>hashtagsCount = hashtagsNum.reduceByKey(lambda a,b:
a+b)
[(‘#good’,2), (‘#weather’, 1)]

The Difference between GroupByKey() and
ReduceByKey()

Example: Word Count
> lines = sc.textFile(“hamlet.txt”)
> counts = lines.flatMap(lambda line: line.split(“ ”))
.map(lambda word => (word, 1))
.reduceByKey(lambda x, y: x + y)
“to be or”
“not to be”
“to”
“be”
“or”
“not”
“to”
“be”
(to, 1)
(be, 1)
(or, 1)
(not, 1)
(to, 1)
(be, 1)
(be, 2)
(not, 1)
(or, 1)
(to, 2)

Basic Actions
>nums = sc.parallelize([1, 2, 3])
# Retrieve RDD contents as a local collection
>nums.collect() # => [1, 2, 3]
# Return first K elements
>nums.take(2) # => [1, 2]
# Count number of elements
>nums.count() # => 3
# Merge elements with an associative function
>nums.reduce(lambda x, y: x + y) # => 6
# Write elements to a text file
>nums.saveAsTextFile(“hdfs://file.txt”)

Collect()
• Return all elements in the RDD to the driver in a single list
• Do not do that if you work on a big RDD.

Reduce()
• Aggregate all the elements of the RDD by applying a user function
pairwise to elements and partial results, and returns a result to the
driver.

Aggregate()
• Aggregate all elements of the RDD by:
• Applying a user function seqOp to combine elements with user-supplied
objects
• Then combining those user-defined results via a second user function
combOp
• And finally returning a result to the driver

Aggregate(): Using the seqOp in each partition

Aggregate(): Using combOp among Partitions

More RDD Operators
• map
• filter
• groupBy
• sort
• union
• join
• leftOuterJoin
• rightOuterJoin
• reduce
�� count
• fold
• reduceByKey
• groupByKey
• cogroup
• cross
• zip
sample
take
first
partitionBy
mapWith
pipe
save ...

Example: PageRank
• Good example of a more complex algorithm
• Multiple stages of map & reduce
• Benefits from Spark’s in-memory caching
• Multiple iterations over the same data

Basic Idea
Give pages ranks (scores) based
on links to them
• Links from many pages  high
rank
• Link from a high-rank page 
high rank
Image: en.wikipedia.org/wiki/File:PageRank-hi-res-2.png

Algorithm
1.0 1.0
1.0
1.0
1. Start each page at a rank of 1
2. On each iteration, have page p contribute
rankp / |neighborsp| to its neighbors
3. Set each page’s rank to 0.15 + 0.85 × contribs

Algorithm
1.0 1.0
1.0
1.0
1
0.5
0.5
0.5
1
0.5

Algorithm
0.58 1.0
1.85
0.58

Algorithm
0.58
0.29
0.29
0.5
1.85
0.58 1.0
1.85
0.58
0.5

Algorithm
0.39 1.72
1.31
0.58
. . .

Algorithm
0.46 1.37
1.44
0.73
Final state:

Machine Learning is…
• Machine learning is about predicting the future based on the past.
-- Hal Daume III
Training
Data
model/
predictor
past
model/
predictor
future
Testing
Data

Supervised vs. Unsupervised Learning

General Flow for Machine Learning

Training Data, Testing Data, Validation Data
• Training data: used to train a model (we have)
• Testing data: test the performance of a model (we don’t have)
• Validation data: “artificial” testing data (we have)

Model Evaluation: What Are We Seeking?
• Minimize the error between training data and the model

Example: The Error of The Model

General Flow of Training and Testing

Supervised Learning in A Nutshell
• Try to think how you learn when you were a baby. Mom taught you…

• What is it?

• Training data • Testing data
Label
Features
Features
Rabbit!
Label
(We Guessed)

Handwritten Recognition
• Input: 1. hand-written words and labels, 2. a hand-written word W
• Output: the label of W
?

What is MLlib
• MLlib is an Apache Spark component focusing on machine
learning:
• MLlib is Spark’s core ML library
• Developed by MLbase team in AMPLab
• 80+ contributions from various organization
• Support Scala, Python, and Java APIs

Algorithms in MLlib
• Statistics: Description, correlation
• Clustering: k-means
• Classification: SVMs, naive Bayes, decision tree, logistic regression
• Regression: linear regression (+lasso, +ridge)
• Dimensionality: SVD, PCA
• Optimization Primitives: SGD, Parallel Gradient
• Collaborative filtering: ALS

Why Mllib
• Scalability
• Performance
• user-friendly documentation and APIs
• Cost of maintenance

Data Type
• Dense vector
• Sparse vector
• Labeled point

Dense & Sparse
• Raw Data:
ID A B C D E F
1 1 0 0 0 0 3
2 0 1 0 1 0 2
3 1 1 1 0 1 1

Dense vs Sparse
• A case study
- number of example: 12 million
- number of features: 500
- sparsity: 10%
• Not only save storage, but also received a 4x speed up
Dense Sparse
Storge 47GB 7GB
Time 240s 58s

Labeled Point
• Dummy variable (1,0)
• Categorical variable (0, 1, 2, …)
from pyspark.mllib.linalg import SparseVector
from pyspark.mllib.regression import LabeledPoint
# Create a labeled point with a positive label and a dense feature vector.
pos = LabeledPoint(1.0, [1.0, 0.0, 3.0])
# Create a labeled point with a negative label and a sparse feature vector.
neg = LabeledPoint(0.0, SparseVector(3, [0, 2], [1.0, 3.0]))

Descriptive Statistics
• Supported function:
- count
- max
- min
- mean
- variance
…
• Supported data types
- Dense
- Sparse
- Labeled Point

Example
from pyspark.mllib.stat import Statistics
from pyspark.mllib.linalg import Vectors
import numpy as np
## example data（2 x 2 matrix at least）
data= np.array([[1.0,2.0,3.0,4.0,5.0],[1.0,2.0,3.0,4.0,5.0]])
## to RDD
distData = sc.parallelize(data)
## Compute Statistic Value
summary = Statistics.colStats(distData)
print "Duration Statistics:"
print " Mean: {}".format(round(summary.mean()[0],3))
print " St. deviation: {}".format(round(sqrt(summary.variance()[0]),3))
print " Max value: {}".format(round(summary.max()[0],3))
print " Min value: {}".format(round(summary.min()[0],3))
print " Total value count: {}".format(summary.count())
print " Number of non-zero values: {}".format(summary.numNonzeros()[0])

Play-Tennis Example
• Given a training set and an unseen sample X = <rain, hot, high, false>,
what class will X be?
Outlook Temperature Humidity Windy Class
sunny hot high false N
sunny hot high true N
overcast hot high false P
rain mild high false P
rain cool normal false P
rain cool normal true N
overcast cool normal true P
sunny mild high false N
sunny cool normal false P
rain mild normal false P
sunny mild normal true P
overcast mild high true P
overcast hot normal false P
rain mild high true N

Try It on Spark
• Download Experimental Data:
https://raw.githubusercontent.com/apache/spark/master/data/mllib/s
ample_naive_bayes_data.txt
• Download the Example Code of Naïve Bayes Classification:
https://raw.githubusercontent.com/apache/spark/master/examples/sr
c/main/python/mllib/naive_bayes_example.py

Experimental Data
0,1 0 0
0,2 0 0
0,3 0 0
0,4 0 0
1,0 1 0
1,0 2 0
1,0 3 0
1,0 4 0
2,0 0 1
2,0 0 2
2,0 0 3
2,0 0 4
Feature Vector: (0,2,0)
Class Label: 1

Naïve Bayes in Spark
• Step 1: Prepare data
• Step 2: NaiveBayes.train()
• Step 3: NaiveBayes.predict()
• Step 4: Evaluation
1
2
3
4
*. Full Version: https://spark.apache.org/docs/latest/mllib-naive-bayes.html

2. Decision Tree
• Decision tree
• A flow-chart-like tree structure
• Internal node denotes a test on an attribute
• Branch represents an outcome of the test
• Leaf nodes represent class labels or class distribution
• Decision tree generation consists of two phases
• Tree construction
• At start, all the training examples are at the root
• Partition examples recursively based on selected attributes
• Tree pruning
• Identify and remove branches that reflect noise or outliers
• Use of decision tree: Classifying an unknown sample
• Test the attribute values of the sample against the decision tree

Example: Predict the Buys_Computer
age income student credit_rating buys_computer
<=30 high no fair no
<=30 high no excellent no
31…40 high no fair yes
>40 medium no fair yes
>40 low yes fair yes
>40 low yes excellent no
31…40 low yes excellent yes
<=30 medium no fair no
<=30 low yes fair yes
>40 medium yes fair yes
<=30 medium yes excellent yes
31…40 medium no excellent yes
31…40 high yes fair yes
>40 medium no excellent no

Decision Tree
age?
overcast
student? credit rating?
no yes fairexcellent
<=30 >40
no noyes yes
yes
30..40

Build A Decision Tree
• Step 1: All data in Root
• Step 2: Split the node which can lead to more pure sub-nodes
• Step 3: Repeat until terminal conditions meet

Measures for Purity
• Information Gain, Gini Index,…
• Example

Decision Tree in Spark
• Step 2: DT.trainClassifier()
• Step 3: DT.predict()
*. Full Version: https://spark.apache.org/docs/latest/mllib-decision-tree.html
1
2
3
4

Ensemble Decision-Tree-based Algorithms
• Random Forest
Pick random subsets to build trees
• AdaBoost
Improve trees sequentially

3. Logistic Regression
• A classification algorithm

Hypotheses function
• hypotheses:

Logistic Regression in Spark
• Step 2: LR.train()
• Step 3: LR.predict()
*. Full Version: https://spark.apache.org/docs/latest/mllib-linear-methods.html#classification
1
2
3
4

4. Support Vector Machine (SVM)
• SVMs maximize the margin around the separating hyperplane.
• The decision function is fully specified by a subset of training samples, the
support vectors.
122
Sec. 15.1

How About Data Are Not Linear Separable?
• General idea: the original feature space can always be mapped to
some higher-dimensional feature space where the training set is
separable.
Sec. 15.2.3
KERNEL
FUNCTION

Kernels
• Why use kernels?
• Make non-separable problem separable.
• Map data into better representational space
• Common kernels
• Linear
• Polynomial K(x,z) = (1+xTz)d
• Radial basis function (RBF)
124
Sec. 15.2.3
RBF

SVM in Spark
• Step 2: SVM.train()
• Step 3: SVM.predict()
1
2
3
4
*. Full Version: https://spark.apache.org/docs/latest/mllib-linear-methods.html#linear-support-vector-machines-svms

AI與大數據數據處理 Spark實戰(20171216)

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