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{{short description|Collection of data}}
[[File:Iris dataset scatterplot.svg|thumb|right|Various plots of the multivariate dataset [[Iris flower data set|''Iris'' flower data set]] introduced by [[Ronald Fisher]] (1936).<ref name="fisher36"/>]]
A '''data set''' (or '''dataset''') is a collection of [[data]]. In the case of tabular data, a data set corresponds to one or more [[table (database)|database tables]], where every [[column (database)|column]] of a table represents a particular [[Variable (computer science)|variable]], and each [[row (database)|row]] corresponds to a given [[Record (computer science)|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.<ref name="Editorial">{{cite journal | last1 = Snijders | first1 = C. | last2 = Matzat | first2 = U. | last3 = Reips | first3 = U.-D. | year = 2012 | title = 'Big Data': Big gaps of knowledge in the field of Internet | url = http://www.ijis.net/ijis7_1/ijis7_1_editorial.html | journal = International Journal of Internet Science | volume = 7 | pages = 1–5 | access-date = 2017-02-10 | archive-date = 2019-11-23 | archive-url = https://web.archive.org/web/20191123051001/http://www.ijis.net/ijis7_1/ijis7_1_editorial.html | url-status = dead }}</ref>
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.<ref>{{Cite web|url=http://www.europeandataportal.eu/data/en/dataset|title=European open data portal|website=European open data portal|publisher=European Commission|access-date=2016-09-23}}</ref>
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The values may be numbers, such as [[real number]]s or [[integer]]s, for example representing a person's height in centimeters, but may also be [[nominal data]] (i.e., not consisting of [[Number|numerical]] values), for example representing a person's ethnicity. More generally, values may be of any of the kinds described as a [[level of measurement]]. For each variable, the values are normally all of the same kind. [[Missing values]] may exist, which must be indicated somehow.
In [[statistics]], data sets usually come from actual observations obtained by [[sampling (statistics)|sampling]] a [[statistical population]], and each row corresponds to the observations on one element of that population. Data sets may further be generated by [[algorithms]] for the purpose of testing certain kinds of [[software]]. Some modern statistical analysis software such as [[SPSS]] still present their data in the classical data set fashion. If data is missing or suspicious an [[imputation (statistics)|imputation]] method may be used to complete a data set.<ref name="sde">{{cite book |title=Statistical Data Editing: Impact on Data Quality: Volume 3 of Statistical Data Editing, Conference of European Statisticians Statistical standards and studies |author=United Nations Statistical Commission |author2=United Nations Economic Commission for Europe |year=2007 |publisher=United Nations Publications |isbn=978-9211169522 |page=20 |url=https://books.google.com/books?id=X0wtLo2XY9gC |access-date=19 July 2015 }}{{Dead link|date=January 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>
== Classics ==
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* [https://data.humdata.org/ Humanitarian Data Exchange(HDX)] – The Humanitarian Data Exchange (HDX) is an open humanitarian [[data sharing]] platform managed by the [[United Nations Office for the Coordination of Humanitarian Affairs]].
* [https://opendata.cityofnewyork.us/ NYC Open Data] – free public data published by New York City agencies and other partners.
* [https://relational.fit.cvut.cz/ Relational data set repository] {{Webarchive|url=https://web.archive.org/web/20180307150058/https://relational.fit.cvut.cz/ |date=2018-03-07 }}
* [https://web.archive.org/web/20190214051201/http://www.researchpipeline.com/mediawiki/index.php?title=Main_Page Research Pipeline] – a wiki/website with links to data sets on many different topics
* [http://lib.stat.cmu.edu/jasadata/ StatLib–JASA Data Archive]
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