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Tidy Data
Tidy data is an alternative name for the common statistical form called a ''model matrix'' or ''data matrix''. A data matrix is defined in as follows: A standard method of displaying a multivariate set of data is in the form of a data matrix in which rows correspond to sample individuals and columns to variables, so that the entry in the ''i''th row and ''j''th column gives the value of the ''j''th variate as measured or observed on the ''i''th individual. Hadley Wickham later defined "Tidy Data" as data sets that are arranged such that each variable is a column and each observation (or ''case'') is a row. (Originally with additional per-table conditions that made the definition equivalent to the Boyce–Codd 3rd normal form.) Data arrangement is an important consideration in data processing, but should not be confused with the also important task of data cleansing. Other relevant formulations include denormalization Denormalization is a strategy used on a previously- norma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Matrix (multivariate Statistics)
In statistics and in particular in regression analysis, a design matrix, also known as model matrix or regressor matrix and often denoted by X, is a matrix of values of explanatory variables of a set of objects. Each row represents an individual object, with the successive columns corresponding to the variables and their specific values for that object. The design matrix is used in certain statistical models, e.g., the general linear model. It can contain indicator variables (ones and zeros) that indicate group membership in an ANOVA, or it can contain values of continuous variables. The design matrix contains data on the independent variables (also called explanatory variables) in statistical models which attempt to explain observed data on a response variable (often called a dependent variable) in terms of the explanatory variables. The theory relating to such models makes substantial use of matrix manipulations involving the design matrix: see for example linear regression. A not ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hadley Wickham
Hadley Alexander Wickham (born 14 October 1979) is a statistician from New Zealand and Chief Scientist at Posit, PBC (former RStudio Inc.) and an adjunct Professor of statistics at the University of Auckland, Stanford University, and Rice University. He is best known for his development of open-source software for the R statistical programming language for data visualisation, including ggplot2, and other tidyverse packages, which support a tidy data approach to data science. Education and career Wickham was born in Hamilton, New Zealand. He received a Bachelors degree in Human Biology and a masters degree in statistics at the University of Auckland in 1999–2004 and his PhD at Iowa State University in 2008 supervised by Di Cook and Heike Hofmann. Wickham is a prominent and active member of the R user community and has developed several notable and widely used packages including ggplot2, plyr, dplyr, and reshape2. Wickham's data analysis packages for R are collectively ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Set
A data set (or dataset) is a collection of data. In the case of tabular data, a data set corresponds to one or more database tables, where every column of a table represents a particular variable, and each row corresponds to a given record of the data set in question. The data set lists values for each of the variables, such as for example height and weight of an object, for each member of the data set. Data sets can also consist of a collection of documents or files. In the open data discipline, data set is the unit to measure the information released in a public open data repository. The European data.europa.eu portal aggregates more than a million data sets. Some other issues ( real-time data sources, non-relational data sets, etc.) increases the difficulty to reach a consensus about it. Properties Several characteristics define a data set's structure and properties. These include the number and types of the attributes or variables, and various statistical measures applic ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boyce–Codd Normal Form
Boyce–Codd normal form (or BCNF or 3.5NF) is a normal form used in database normalization. It is a slightly stronger version of the third normal form (3NF). BCNF was developed in 1974 by Raymond F. Boyce and Edgar F. Codd to address certain types of anomalies not dealt with by 3NF as originally defined.Codd, E. F. "Recent Investigations into Relational Data Base" in ''Proc. 1974 Congress'' (Stockholm, Sweden, 1974). New York, N.Y.: North-Holland (1974). If a relational schema is in BCNF then all redundancy based on functional dependency has been removed, although other types of redundancy may still exist. A relational schema ''R'' is in Boyce–Codd normal form if and only if for every one of its dependencies ''X → Y'', at least one of the following conditions hold: * ''X'' → ''Y'' is a trivial functional dependency (Y ⊆ X), * ''X'' is a superkey for schema ''R''. 3NF table always meeting BCNF (Boyce–Codd normal form) Only in rare cases does a 3NF table not meet the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Cleansing
Data cleansing or data cleaning is the process of detecting and correcting (or removing) corrupt or inaccurate records from a record set, table, or database and refers to identifying incomplete, incorrect, inaccurate or irrelevant parts of the data and then replacing, modifying, or deleting the dirty or coarse data. Data cleansing may be performed interactively with data wrangling tools, or as batch processing through scripting or a data quality firewall. After cleansing, a data set should be consistent with other similar data sets in the system. The inconsistencies detected or removed may have been originally caused by user entry errors, by corruption in transmission or storage, or by different data dictionary definitions of similar entities in different stores. Data cleaning differs from data validation in that validation almost invariably means data is rejected from the system at entry and is performed at the time of entry, rather than on batches of data. The actual process of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Denormalization
Denormalization is a strategy used on a previously- normalized database to increase performance. In computing, denormalization is the process of trying to improve the read performance of a database, at the expense of losing some write performance, by adding redundant copies of data or by grouping data.S. K. Shin and G. L. SandersDenormalization strategies for data retrieval from data warehouses Decision Support Systems, 42(1):267-282, October 2006. It is often motivated by performance or scalability in relational database software needing to carry out very large numbers of read operations. Denormalization differs from the unnormalized form in that denormalization benefits can only be fully realized on a data model that is otherwise normalized. Implementation A normalized design will often "store" different but related pieces of information in separate logical tables (called relations). If these relations are stored physically as separate disk files, completing a database qu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semantic Triple
A semantic triple, or RDF triple or simply triple, is the atomic data entity in the Resource Description Framework (RDF) data model. As its name indicates, a triple is a set of three entities that codifies a statement about semantic data in the form of subject–predicate–object expressions (e.g., "Bob is 35", or "Bob knows John"). Subject, predicate and object This format enables knowledge to be represented in a machine-readable way. Particularly, every part of an RDF triple is individually addressable via unique URIs — for example, the statement "Bob knows John" might be represented in RDF as: http://example.name#BobSmith12 http://xmlns.com/foaf/0.1/knows http://example.name#JohnDoe34. Given this precise representation, semantic data can be unambiguously queried and reasoned about. The components of a triple, such as the statement "The sky has the color blue", consist of a subject ("the sky"), a predicate ("has the color"), and an object ("blue"). This is similar to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
