The machine learning algorithm t-Distributed Stochastic Neighborhood Embedding, also abbreviated as t-SNE, can be used to visualize high-dimensional datasets. Each high-dimensional information of a data point is reduced to a low-dimensional representation. However, the information about existing neighborhoods should be preserved.
So this technique is another tool you can use to create meaningful groups in unordered data collections based on the unifying data properties. If you don’t know what cluster algorithms are, check out this article. Here we present 5 machine learning methods that you should know. As shown in the following figure, the data should be represented grouped in 2-dimensional space.
But how does the algorithm work and what are its strengths? In order to understand its function, we need to look at the origin of the technology.
What is the Stochastic Neighbor Embedding (SNE) Algorithm?
The basis of the t-Distributed Stochastic Neighborhood Embedding algorithm is originally the Stochastic Neighbor Embedding (SNE) algorithm. This converts high-dimensional Euclidean distances into similarity probabilities between individual data points. The probability with which an object occurs next to a potential neighbor must be calculated. The dissimilarities between two high-dimensional data points can be explained with a distance matrix, corresponding to the squared Euclidean distance. A conditional probability is calculated for the low-dimensional correspondence. This determines the similarity of the two data points on the low-dimensional map.
In order to achieve the closest possible correspondence between the two distributions pij and qij, a Kullback-Leibler divergence (KL) over all neighbors of each data point is computed as a cost function C. Large costs are incurred for distant data points.
A gradient descent method is used to optimize the cost function. However, this optimization method converges very slowly. In addition, a so-called crowding problem arises.
If a high dimensional data set is linearly approximated in a small scale, then it cannot be reduced to a lower dimension with a local scaling algo- rithm to a lower dimension.
What makes the t-Distributed Stochastic Neighborhood Embedding (t-SNE) Algorithmt work?
The t-Distributed Stochastic Neighbor Embedding (t-SNE) algorithm starts here. On the one hand, a simplified symmetric cost function is used.
Here, only one KL is minimized over a common probability distribution of all high, and low dimensional data is minimized.
On the other hand, the similarity of the low-dimensional data points is computed with a Student’s t-distribution and a degree of freedom of one. This can be optimized quickly and is stable to the crowding problem. stable against the crowding problem.
There is a lot of Big Data software available now. One of them that you should definitely know about is the H2O AI Machine Learning solution.
With this open-source application you can implement algorithms from the fields of statistics, data mining and machine learning. The H2O AI Engine is based on the distributed file system Hadoop and is therefore more performant than other analysis tools. Your machine learning methods can thus be used as parallelized methods.
They can program their algorithms in R, Python and Java and thus in the most important mathematical programming languages. H2O provides a REST interface to Python, R, JSON and Excel. Additionally, you can access H2O directly with Hadoop and Apache Spark. This makes integration into your data science workflow much easier. You already get approximate results while running the algorithms. A graphical web browser UI helps you to better analyze the processes and perform targeted optimizations.
How Clients Interacts with H2O AI
You can interact with H2O via clients using various interfaces. It is important for you to know that the data is usually not held in memory. They are localized in a H2O cluster and you only get a pointer to the data when you make a request.
The basic unit of data storage accessible to you is the H2O Frame. This corresponds to a two-dimensional, resizable and potentially heterogeneous data point. This tabular data structure also contains labeled axes.
Your H2O cluster consists of one or more nodes. A node corresponds to a JVM process and this process consists of three layers.
H2O Machine Learning Components
The R evaluation layer is a slave to the REST client front-end and in the Scala layer you can write native programs and algorithms. You can then use these with H2O Machine learning.
This layer is where your algorithms are applied. You can run statistical methods, data import and machine learning here.
In this layer you handle the resource management. You can manage both the memory and the CPU processing capacity.
As a data scientist, you have several basic tools at your disposal, which you can also apply in combination to a data set. Here we present some clustering algorithms that you should definitely know and use
In times of Big Data, not only the sheer number of data increases, but also the relationships between them. More and more complex dependencies are formed. This makes it all the more difficult to recognize these similar properties and to assign the data to so-called clusters in a way that can be evaluated.
You have certainly heard of these algorithms and maybe used one or the other, but do you really know what clustering algorithms are?
What are clustering algorithms?
So let’s first clarify what these algorithms are in the first place. The goal is clear: You want to identify similar properties between individual data points in a data set and group them in a meaningful way. These properties are often high-dimensional.
With the help of cluster analysis, you want to reduce this high-dimensional information to a low-dimensional dependency. So, for example, a representation in 2D space. Clustering is an unsupervised machine learning technique and in the end you classify the data points by using algorithms.
The approach to clustering differs from technique to technique. All have their advantages and disadvantages, so it makes sense to try several on one set of data, or apply them in combination. Below we will introduce you to some popular clustering methods and explain their grouping approach.
The first algorithm we want to introduce you to is Mean-Shift Clustering. With this you can find dense areas of data points according to the concept of kernel density estimation (KDE). The basis of the clustering is a circular sliding window, which moves towards higher density at each iteration. Within the window, the centers of each class are determined, called centroids.
The movement is now created by moving the center to the average of the points within the window. The density within the sliding window is thus proportional to the number of points within it. This motion continues until there is no direction in which the motion can take more points within the kernel.
Hierarchical Cluster Analysis (HCA)
With HCA, clusters are formed based on empirical similarity measures of the data points. This means that the two most similar objects are assigned one after the other until all objects are in one cluster. This results in a tree-like structure. In contrast to the K-means algorithm, which we will discuss later, similarities between the clusters play a role. These are represented by a cluster distance. With K-means, only all objects within a collection are similar to each other, while they are dissimilar to objects in other clusters.
You can create an HCA in different ways. There are two elementary procedures, the top-down and the bottom-up. If you want to know more about Hierarchical Cluster Analysis, read this article.
Expectation-Maximization (EM) Clustering using Gaussian Mixture Models (GMM)
GMM basically assumes that the data points are Gaussian and not circular. The clusters are described by their mean and standard deviation. Each Gaussian distribution is randomly assigned to a single cluster and found using the Expectation-Maximization (EM) optimization algorithm. The probability of belonging to a cluster is then calculated for each data point. Thus, the closer a point is to the Gaussian center, the more likely it is then to belong to that cluster. Based on these probabilities, a new set of parameters for the Gaussian distributions is iteratively calculated. That is, the probabilities within a cluster are maximized.
K-Means clustering algorithms
The k-Means algorithm described by MacQueen, 1967 goes back to the methods described by Lloyd, 1957 and Forgy, 1965. You can use the algorithm besides cluster analysis also for vector quantization. Here, a data set is partitioned into k groups with equal variance.
The number of clusters must be specified in advance. Each disjoint cluster is described by the average of all contained samples. The so-called cluster centroid.
Each centroid is updated to represent the average of its constituent instances. This is done until the assignment of instances to the clusters does not changes any more. If you want to learn more about the K-means algorithm, check this out.
Density-Based Spatial Clustering of Applications with Noise (DBSCAN)
DBSCAN is a density-based cluster analysis with noise. From an arbitrary starting data point, neighborhood points are specified at a distance epsilon. Clustering then begins from a certain neighborhood data point count.
The current data point becomes the first point of the new cluster, or referred to as noise. In both cases, however, it is considered to be examined. The neighboring data points are then added to the cluster. Once all neighbors have been added, a new, unexamined point is called and processed. A new cluster is thus formed.
The field of cluster algorithms is wide and everyone’s approach is different. You should be aware that there is no one solution. You have to consider each algorithm as another tool. Not every technique works equally well in every situation.
The key here is to always understand the basic approach of each algorithm you want to use. Build a small portfolio and get to know these techniques well. Once you master them, you should then add new ones. Knowing your own tools is crucial to avoid try and error and to gain control over your data. Remember: no result is a result. Your added value here is that even if an algorithm doesn’t work well on your data set, it will give you information about the data properties.
Data Mining vs Big Data Analytics – Both data disciplines, but what makes them different? In this article, we introduce you to both fields and explain the key differences.
Data Science is an interdisciplinary scientific field, as it has become more and more in focus in the last decades. Many companies see this as the key to an Industry 4.0 company. The hope is that valuable information can be found in the company’s own data, which can be used to massively increase its own profitability. Terms such as big data, data mining, data analytics and machine learning are being thrown into the ring. Many people do not realize that these terms describe other disciplines. If you want to build a house, you need the right tools and you have to know how to use them.
Map of Data Disciplines
First of all, you should think of the individual disciplines as being layered into each other like an onion. So there is overlap between all the fields and when you talk about a discipline, you are also talking about lower layers.
Since data analytics is located above data mining in the layer model, it is already clear that mining must be a sub discipline of analytics. Therefore, we will first describe the comprehensive discipline.
Data Mining vs Big Data Analytics – What is Analytics?
Big data analytics, as a sub field of data analysis, describes the use of data analysis tools and without special data processing. in data analytics, you use queries and data aggregation methods, but also data mining techniques and tools. The goal of this discipline is to represent various dependencies between input variables.
The goal of this discipline is to represent various dependencies between input variables. The following figure shows the individual overlaps in the use of the tools of the different disciplines.
Data Mining vs Big Data Analytics – What is Data Mining?
Data mining is a subset of data analytics. At its core, it is about identifying and discovering a large data set through correlations. Especially if you know little about the available data this field should be used.
But what does a typical data mining process look like and what are typical data mining tasks?
Data Mining Process
You can divide a typical data mining process into several sequential steps. In the preprocessing stage, your data is first cleaned. This involves integrating sources and removing inconsistencies. Then you can convert the data into the right format. After that, the actual analysis step, the data mining, takes place.Finally, your results have to be evaluated. Expert knowledge is required here to control the patterns found and the fulfillment of your own objectives.
The term data mining covers a variety of techniques and algorithms to analyze a data set. In the following we will show you some typical methods.
Data Mining Tasks
Besides identifying unusual data sets with outlier detection, you can also group your objects based on similarities using cluster analysis. In this article we have already summarized some popular clustering algorithms that you should know as a data scientist. While association analysis only identifies the relationships and dependencies in the data, regression analysis provides you with the relationships between dependent and independent variables. Through classification, you assign elements that were not previously assigned to classes to existing classes. You can also summarize the data to reduce the data set to a more compact description without significant loss of information.
Data Mining vs Big Data Analytics – Conclusion
Although the two disciplines are related, they are two different disciplines. Data mining is more about identifying key data relationships, patterns or trends in the data, while data analytics is more about deriving a data-driven model. On this path, data mining is an important step in making the data more usable. In the end, it’s not a versus, but both disciplines are part of an analytics pipeline. In this article, we will go further into the differences between the various data sciences and clarify the difference between data analysis and data science.
In this article we will explain everything you need to know about Apache Avro, an open source big data serialization solution and why you should not do without it.
You can serialize data objects, i.e. put them into a sequential representation, in order to store or send them independent of the programming language. The text structure reflects your data hierarchy. Known serialization formats are for example XML and JSON. If you want to know more about both formats, read our articles on the topics. To read, you have to deserialize the text, i.e. convert it back into an object.
In times of Big Data, every computing process must be optimized. Even small computing delays can lead to long delays with a correspondingly large data throughput, and large data formats can block too many resources. The decisive factors are therefore speed and the smallest possible data formats that are stored. Avro is developed by the Apache community and is optimized for Big Data use. It offers you a fast and space-saving open source solution. If you don’t know what Apache means, look here. Here we have summarized everything you need to know about it and introduce you to some other Apache open source projects you should know about.
Apache Avro – Open Source Big Data Serialization Solution
With Apache Avro, you get not only a remote procedure call framework, but also a data serialization framework. So on the one hand you can call functions in other address spaces and on the other hand you can convert data into a more compact binary or text format. This duality gives you some advantages when you have cross-network data pipelines and is justified by its development history.
Avro was released back in 2011 as a part of Apache Hadoop. Here, Avro was supposed to provide a serialization format for data persistence as well as a data transfer format for communication between Hadoop nodes. To provide functionality in a Hadoop cluster, Avro needed to be able to access other address spaces. Due to its ability to serialize large amounts of data, cost-efficiently, Avro can now be used Hadoop-independently.
You can access Avro via special API’s with many common programming languages (Java, C#, C, C++, Python and Ruby). So you can implement it very flexible.
In the following figure we have summarized some reasons what makes the framework so ingenious. But what really makes Avro so fast?
What makes Avro so fast?
The trick is that a schema is used for serialization and deserialization. About that the data hierarchy, i.e. the metadata, is stored separately in a file. The data types and protocols are defined via a JSON format. These are to be assigned unambiguously by ID to the actual values and can be called for the further data processing constantly. This schema is sent along with the data exchange via RPC calls.
Creating a schema registry is especially useful when processing data streams with Apache Kafka.
Apache Avro and Apache Kafka
Here you can save a lot of performance if you store the metadata separately and call it only when you really need it. In the following figure we have shown you this process schematically.
When you let Avro manage your schema registration, it provides you with comprehensive, flexible and automatic schema development. This means that you can add additional fields and delete fields. Even renaming is allowed within certain limits. At the same time, Avro schema is backward and forward compatible. This means that the schema versions of the Reader and Writer can differ. Schema registration management solutions exist, with Google Protocol Buffers and Apache Thrift, among others. However, the JSON data structure makes Avro the most popular choice.
What does HCA stand for? What is the difference between Agglomerative and Divisive? When do I use the algorithm and what are its strengths? In this article we will clarify all these questions.
If you don’t know what clustering means, check out this article. Here we also explain four other clustering methods that you as a data scientist must know.
What is an HCA?
Hierarchical Cluster Analysis, or HCA, is a technique for optimal and compact connection of objects based on empirical similarity measures. The two most similar objects are assigned one after another until all objects are finally in one cluster. This then results in a tree-like structure.
So how does a hierarchical cluster procedure work?
Agglomerative vs Divisive Calculation
The basic clustering can be done in two opposite ways, Agglomerative and Divisive calculation.
Agglomerative Nesting, abbreviated AGNES, is also known as the bottom-up method. This method first creates a cluster between two objects with high similarity, and then adds more clusters until all the data has been enclosed.
The divisive cluster calculation follows an opposite concept.
Divisive hierarchical clustering:
Divise Analysis, also known as DIANA, is a top-down method. All objects are directly framed into a cluster and then reduced in size.
In the following figure, the agglomerative process is compared with the divisive process.
Thus, the goal is to represent the common properties in low dimension in multidimensional raw data. A strength of this machine learning method is the inclusion of cluster relationships. With K-means, only all objects within a collection are similar to each other, while they are dissimilar to objects in other clusters. If you want to know more about this other popular clustering method, read this article.
How to calculate the cluster distances?
As mentioned earlier, not only are similarities between data points in a cluster weighted, but also similarities between groups. These similarities are represented by distances between the clusters. These distances can be determined in different ways. The distance between the centroids of two clusters can be calculated. A single linkage is the shortest distance between two clusters, a complete linkage is the largest distance between two clusters and an average linkage is the average distance between two clusters.
The figure below contrasts each cluster distance calculation method.
In addition to the planar representation, the HCA can also be represented in a dendrogram.
HCA represented in a Dendrogram
Since an HCA describes a tree structure, it can be well represented in a dendrogram. Here the connections between the individual data elements and the connections between the clusters become well visible. This diagram can help to choose the optimal number of clusters in the data depending on where you intersect the tree.
In the following figure, for example, such a dendrogram is shown in dependence on Agglomerative and Divisive Calculation.
One of the most popular unsupervised clustering methods is the k-means algorithm. It is considered one of the easiest and most cost-effective clustering algorithms to create. It is therefore well suited to identify an overview of possible patterns in data.
What is the principle behind the k-means algorithm? in this article we will explain what is behind this algorithm and how it really works, because, the better you know your data science tools, the better you will be able to analyze your data.
What is k-Means?
The k-means algorithm described by MacQueen, 1967 goes back to the methods described by. Lloyd, 1957 and Forgy, 1965 described methods. The unsupervised machine learning algorithm is used for vector quantification or cluster analysis. If you don’t know what the differences are between supervised, unsupervised and reinforcement methods, read this article on the main machine learning categories.
The following figure shows the basic principle of the k-Means clustering algorithm.
The main goal of unsupervised clustering is to create collections of data elements that are similar to each other, but dissimilar to elements in other clusters.
What is the principle behind the k-means algorithm?
Here, a data set is partitioned into k groups with equal variance. The number of clusters searched for must be specified in advance. Each disjoint cluster is described by the average of all contained samples. The so-called cluster centroid. The following figure shows the cluster center of gravity principle.
Each centroid is updated to represent the average of its constituent instances. This is done until the assignment of instances to clusters does not change.
Applied algorithm process
But how exactly does the algorithm work? First, initial centroids are set. The distances between data instances and centroids are measured and data instances are added as members of the nearest centroid. The centroids are recalculated. If necessary, final centroids are re-measured, re-clustered or re-calculated
A perceptron is a simple binary classification algorithm modeled after the biological neuron and is thus a very simple learning machine. The output function here is determined by the weighting of the inputs and by the thresholds. Perceptrons are used for machine learning as well as for artificial intelligence (AI) applications. If you don’t know the difference between AI, neural networks and machine learning you should read our article on the subject.
What does the learning process look like?
A set of input signals are decomposed into a binary output decision, i.e. zeros or ones. By training with certain input patterns, similar patterns can thus be found in a data set to be analyzed. The following figure shows this learning process schematically.
If a set threshold is exceeded or not reached by weighting all inputs, the state of the neuron output changes. If one now trains a perceptron with given data patterns, the weighting of the inputs changes. The perceptron thus has the ability to learn and solve complex problems by adjusting the weights.
However, a basic requirement to obtain valid results is that the data must be linearly separable.
What are Multilayer Perceptrons (MLP)
A multilayer perceptron corresponds to what is known as a neural network. Perceptrons thus form the neuronal base, which are interconnected in different layers.
The figure below shows a simple three-layer MLP. Each line here represents a different output.
However, neurons of the same layer have no connections to each other. For each signal, the perceptron uses different weights and the output of a neuron is the input vector of a neuron of the next layer. The diversity of classification possibilities increases with the number of layers.
Recurrent Neural Networks vs Feed-Forward Networks
Basically, neural networks are distinguished according to the recurrent and the feed-forward principle.
Recurrent Neural Networks
In the recurrent neural network the neurons are connected to neurons of the same or a preceding layer. Here, a basic distinction is made between three types of feedback. With the direct feedback the own output of a neuron is used as further input. In indirect feedback, on the other hand, the output of a neuron is connected to a neuron of the preceding layers. In the last feedback principle, lateral feedback, the output of a neuron is connected to another neuron of the same layer.
In feed-forward networks, on the other hand, the outputs are connected only to the inputs of a subsequent layer. These can be fully connected, then the neurons of a layer are connected to all neurons of the directly following layer. Or short-cuts are formed. Some neurons are then not connected to all neurons of the next layer.
Data Warehousing – In today’s flood of data, it is becoming increasingly difficult to maintain a clear data management system. More and more data sources are recorded via different software systems. A unified, centralized system can facilitate analysis and ensure that only one data truth exists in an organization.
What is a Data Warehouse System?
Data warehouse systems are built by integrating data from multiple heterogeneous sources and, in addition to centralization, performs the task of structuring data, supporting analytical reporting and structuring decision-making. The system can perform data cleansing as well as data integration and data consolidation and does not require transaction processing or recovery.
It is thus a powerful Big Data information system that can centrally handle everything related to data processing.
What does a Data Warehouse structure look like?
The term data warehouse is used to describe various architectures and systems. However, multi-layer architectures are typical. In this article, we will introduce you to the most commonly used three-tier architecture. If you are interested in the different types, you should read this article from us on the topic. Here we present the individual types in detail.
This article is primarily about what the advantages of the system actually are and how the data communication works.
Data Warehousing Features
Data warehousing offers several features. Such an information system is subject oriented. It does not focus on the current operation, as these data are separated. This means that frequent changes in the operational database are not reflected in the data warehouse. Thus, the focus is on modeling and analysis of data. The system is Time variant, which means that the collected data are identified with a certain period of time and previous data are not deleted when new data are added.
However, some terms that often come up in connection with this system need to be clarified. When metadata is mentioned, a kind of roadmap to the data warehouse is meant. Here the warehouse objects are defined and it acts as a directory. This means that the decision support system finds the contents via the metadata.
The metadata is stored in the metadata repository. An integral directory that manages both the business metadata, i.e. data ownership information, business definition and change policies, and the operational metadata. Operational metadata refers to the timeliness of the data is it active, archived or cleansed, and data lineage, which is the history of the data. This includes the data used to map the operational environment, source databases and their contents, data extraction, data partitioning, cleansing, transformation rules, data refreshing and cleansing rules, but also the algorithms for summation, dimensional algorithms, data for granularity, aggregation, summation, etc.
The so-called data cube represents data in multiple dimensions and the data mart contains only the data specific to a certain group.
Load Data into Warehouse
In addition to the different components and architectures, data can also be transmitted to the information system in different ways.
As shown in the figure, a basic distinction is made between two elementary processes.
What is ELT?
Extract, Load, and Transform, or ELT for short, is about extracting aggregate information from the source system and loading it into the target method.
The following figure shows such an example system. In this case, the Hadoop framework handles the central data management, while applications and analysis tools access the untransformed data.
What is ETL?
In Extract, Transform and Load, or ETL for short, the data set is first extracted from the sources into a staging area, then transformed or reformatted with business manipulation performed on it, and only then loaded into the target or destination database or data warehouse.