# Data set

A data set (or dataset) is a collection of data, usually presented in tabular form. Each column represents a particular variable. Each row corresponds to a given member of the data set in question. It lists values for each of the variables, such as height and weight of an object or values of random numbers. The data set may comprise data for one or more members, corresponding to the number of rows.

Historically, the term originated in the mainframe field, where it had a well-defined meaning, very close to contemporary computer file. This topic is not covered here.

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. More generally, values may be of any of the kinds described as a level of measurement. 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.

## Classic data sets

Several classic data sets have been used extensively in the statistical literature: 