csdn：https://blog.csdn.net/linxid/article/details/80494922

Chapter1 Introduction

1.1 What is Big Data:

Answer： used to describe a massive structured and unstructured data that is so large that it is difficult to process using traditional database and software techniques.

1.2 4V of Big Data:

Answer： Volume:大量; Velocity:快速；Variety:多样; Veracity:真实准确。

1.3 Knowledge Discovery from Data (KDD)

1. Data cleaning (to remove noise and inconsistent data)
2. Data integration (where multiple data sources may be combined)
3. Data selection (where data relevant to the analysis task are retrieved from the
   database)
4. Data transformation (where data are transformed and consolidated into forms
   appropriate for mining by performing summary or aggregation operations)4
5. Data mining (an essential process where intelligent methods are applied to extract
   data patterns)
6. Pattern evaluation (to identify the truly interesting patterns representing knowledge
   based on interestingness measures—see Section 1.4.6)
7. Knowledge presentation (where visualization and knowledge representation techniques are used to present mined knowledge to users)

1.4 What is Data mining:

Answer： Under acceptable computational efficiency limitations, applying data analysis
and discovery algorithms, to produce a particular enumeration of patterns over the
data

1.5 Main Data Mining Tasks:

Answer：
1. Association rule mining (Two Steps: Find All Frequent itemsets, Generate strong association rules from frequent itemsets),
Finding frequent patterns, associations, correlations, or causal structures among sets of items or objects in transaction databases, relational databases, and other information repositories.

1. Cluster analysis (Methods: Partitioning method, Hierarchical method, Density-Based method, and Grid-Based method),
2. Classification/Prediction,
3. Outlier detection

Chapter2 Basic Concepts

2.1 Tasks of ML:

Answer：
supervised learning; Unsupervised learning; Semi-supervised learning

2.2 How to avoid Overfitting:

Answer：
Increase Sample; Remove outliers； Decrease model complexity,train-validation-test (cross validation),regularization

2.3 Basic Algorithm：

2.3.1 Classification:

KNN；Naive Bayes；Decision Tree；SVM；

2.3.2 Ensemble Learning：

Bagging -> Random Forest；Boosting -> AdaBoost；Stacking；

2.3.3 Clustering:

K-means；Hierarchical Clustering；DBSCAN；Apriori;

Chapter3 Hashing

Why we need Hashing?

To resolve the challenge, like the curse of dimensionality, storage cost, and query speed.

3.1 Find Similar Items

3.1.1 Shingling

• k-Shingling

3.1.2 Minhashing

Definition: the number of the first row in which column

• Jaccard Similarity of Sets
• From sets to Boolean Matrices
• Signatures –> Signature Matrix
• Hashing Function

How to compute the Signature matrix

3.1.3 Locality Sensitive Hashing(LSH)

References：

https://blog.csdn.net/linxid/article/details/79745964

Chapter4 Sampling for Big Data

4.1 Why we need sampling:

sampling is the selection of a subset (a statistical sample) of individuals from within a statistical population to estimate characteristics of the whole population.

Two advantages of sampling:

the cost is lower and data collection is faster than measuring the entire population.

The Problem: generating values if X which are distributed according to the distribution.

4.2 Basics of Sampling

4.2.1 Inverse Transfrom Sampling

samling based on the inverse of Cumulative Distribution Function

Algorithm:
* 1.Generate a random number u from the standard uniform distribution in the interval [0,1].
* 2.Compute the value x such that Fx(x) = u.
* 3.Take x to be the random number drawn from the distribution described by Fx.

Drawbacks: It is hard to get the inverse function.

4.2.2 Rejection Sampling

The problem of Rejection Sampling can be solved by using Adaptive Rejection sampling.
Algorithm:
* 1.Obtain a sample y from proposal distribution Y and a sample u from Uniform(0,1)(the uniform distribution over the unit interval).
* 2.If u

4.2.3 Importance Sampling

Not reject but assign weight to each instance so that the correct distribution is targeted.

4.2.4 Rejection Sampling VS Importance Sampling:

• Instances from RS share the same “weight”, only some of instances are reserved
• Instances from IS have different weight, all instances are reserved
• IS is less sensitive to proposal distribution

4.3 MCMC(Markov chain Monte Carlo)

Markov property:
If the conditional probability distribution of future states of the process depends only upon the present state.

Markov chain:
A Markov chain is a sequence of random variables x1,x2,x3…with Markov property.

4.3.1 MH(Metropolis-Hastings) Sampling：

4.3.2 Gibbs Sampling：

4.3.3 Gibbs V.S. MH

MH Sampling:
* Doesn’t have a 100% acceptance rate
* Doesn’t require to know the full conditionals
* Acceptance threshold would be very crucial

Gibbs Sampling:
* 100% acceptance rate
* Need to know the full conditionals

References：

https://blog.csdn.net/itplus/article/details/19168937
https://blog.csdn.net/google19890102/article/details/51755242
https://en.wikipedia.org/wiki/Sampling_(statistics)
https://blog.csdn.net/ustbxy/article/details/45458725
https://blog.csdn.net/baimafujinji/article/details/51407703
《Pattern Recognition and Machine Learning》Bishop

Chapter5 Data Stream

5.1 What is Data Stream

what is the challenge of the Data Stream:

• Single Pass Handling
• Memory limitation
• Low Time complexity
• Concept Drift

5.2 What is Concept Drift

Concept drift means that the statistical properties of the target variable, which the model is trying to predict, change over time in unforeseen ways.

the probability distribution changes.

Real concept drift:
p(y|x) changes

Virtual concept drift:
p(x)changes,but not p(y|x)

5.3 Concept drift detection:

5.3.1.distribution-based detector

Monitoring the change of data distributions

Disadvantage:

• Hard to determine window size
• learn concept drift slower
• virtual concept drift

5.3.2.Error-rate based detector:

based on the change of the classification performance.

Disadvantage:

• Sensitive to noise
• Hard to deal with gradual concept drift
• Depend on learning model itself heavily

Drift detection method:DDM

5.4 Data Stream Classification:

Data stream classification circle:

• Process an example at a time, and inspect it only once
• Be ready to predict at any point
• Use a limited amount of memory
• Work in a limited amount of time

5.4.1 VFDT(Very Fast Decision Tree)

Algorithm:
* calculate the information gain for the attributes and determines the best two attributes
* At each node,check for the condition: delta(G) = G(a) - G(b) > e
* if condition satisfied, create child nodes based on the test at the node.
* if not, stream in more examples and perform calculations till condition satisfied.

Strengths:
* Scale better than traditional methods
* incremental

Weakness:
* Could spend a lot of time with times
* Memory used with tree expansion
* Number of candidate a

5.5 Data Stream Clustering:

Data stream clustering Framework:

Online Phase:

Summarize the data into memory-efficient data structures

Offline Phase:

Use a clustering algorithm to find the data partition

References：

https://machinelearningmastery.com/gentle-introduction-concept-drift-machine-learning/
http://www.liaad.up.pt/kdus/products/datasets-for-concept-drift
https://www.hindawi.com/journals/tswj/2015/235810/

Chapter6 Graph Mining

6.1 BackGround:

Applications in real-world:

• information Maximization
• computer network security
• prediction

Network types:

• regular
• Random
• small world
• scale free

Six degree of separation:

The average distance between two random individuals in the USA: 6

The average distance between two randomly users in Facebook(721 million active users, 69 billion links): 4.74

6.2 Key Node Identification

6.2.1 Centrality:

• Degree Centrality
• Between Centrality
• Closeness Centrality

6.2.2 K-shell Decomposition:

Advantage:

• Low computational complexity
• Reveal the hierarchy structure clearly

Disadvantage:

• Can not use in a lot of networks
• Too coarse, sometimes is inferior to degree measure.

Explation:

Prune all the nodes with degree 1 till no degree 1 nodes left in the network, the nodes pruned have ks=1. Similarly, prune other nodes having degree 2 and assign them ks =2. Repeat, till the graph becomes empty.

6.2.3 PageRank:

If a page is linked with many high-cited pages, then it will gain high PageRank score.
We assume a customer can use URL to link to any pages, to solve the problem that a node has no outlinks.

the equation of a Page’s PR:

Explanation:

http://blog.jobbole.com/23286/

https://www.cnblogs.com/rubinorth/p/5799848.html

https://en.wikipedia.org/wiki/PageRank#Algorithm

6.3 Community Detection

How to find intrinsic Community structure in large-scale networks:

• Minimum cut:
  may return an imbalanced partition.

• Ratio Cut & Normalized cut:
  How to calculate Ratio Cut and Normalized Cut.We can use spectral clustering algorithm to calculate it.

• Modularity Maximization:
  measure the strength of a community by taking into account the degree distribution.

A new viewpoint for community detection

References：

http://blog.sciencenet.cn/blog-3075-982948.html

Chapter7 Hadoop-Spark

7.1 Hadoop

7.1.1 What is Hadoop

Definition：

Hadoop is a software framework for distributed processing of large datasets across large clusters of computers.

Design principles

• Automatic parallelization & distribution
• fault tolerance and automatic recovery
• clean and simple programming abstraction

Hadoop Architecture:

• Distributed file system (HDFS)
• Execution engine (MapReduce)
  

7.1.2 HDFS(Hadoop Distributed File System)

What is HDFS:

The HDFS is a distributed, scalable, and portable file system written in Java for the Hadoop framework

Namenode(名称结点):

Datanodes(数据结点)：

Main properties of HDFS:

• Large: A HDFS instance may consist of thousands of server machines
• replication: Each data block is replicated many times
• failure: Failure is the norm rather than exception
• fault tolerance: Detection of faults and quick, automatic recovery from them is a core architectural goal of HDFS

Hadoop vs other systems:

Hadoop is a software framework for distributed processing of large datasets across large clusters of computers

7.1.2 Design principles

Automatic parallelization & distribution, fault tolerance and automatic recovery, clean and simple programming
abstraction
* Main properties of HDFS
Large, replication, failure, fault tolerance
* Hadoop vs other systems

Distributed database	Hadoop
Computing model	Transactions, concurrency control
Data model	Sturcture data, read/write mode
Cost model	Expensive
Fault tolerance	Rare
Key characteristics	Efficiency, optimizations, fine-tuning

7.1.3 MapReduce

What is MapReduce:

MapReduce is a programming model and an associated implementation for processing and generating big data sets with a parallel, distributed algorithm on a cluster.

Users only provide the “Map” and “Reduce” functions.

How it Works:

Example:

7.2 Spark

MapReduce limitations:

• Great at one-pass computation, but inefficient for multi-pass algorithms.
• No efficient primitives for data sharing

Spark’s Goal:

Generalize MapReduce to support new apps within same engine

MapReduce VS Spark:

• MapReduce limitations
  Great at one-pass computation, but inefficient for multi-pass algorithms.
  No efficient primitives for data sharing
• Spark’s Goal
  Generalize MapReduce to support new apps within same engine

MapReduce VS Spark**

MapReduce	Spark
Great at one-pass computation, but inefficient for multi-pass algorithims	Extends programming languages with a distributed collection data-structure (RDD)
No efficient primitives for data sharing	Clean APIs in Java, Scala, Python, R

References：

https://www.yiibai.com/hadoop/hadoop_introduction_to_hadoop.html
https://blog.csdn.net/qq_26437925/article/details/78467216