Data set

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A data set (or dataset) is a collection of data, usually presented in tabular form. Each column represents a particular variable, and each row is an assignment of values for each of the variables to a member of the set in question.

In the simplest case, there is only one variable, and then the data set consists of a single column of values, often represented as a list.

The values may be numbers, such as real numbers or integers, for example representing a person's height in centimeters, but may also be nominal data (i.e., not consisting of numerical values), for example representing a person's ethnicity. For each variable, the values will normally all be of the same kind. However, there may also be "missing values", which need to be indicated in some way.

In statistics data sets usually come from actual observations obtained by 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.

While the term suggests a relationship to set theory it should not be assumed that a given data set is, in fact, a set in the usual mathematically sense. The rows of a data set need not be distinct, and so a data set is technically a multiset.