Editing Compositional data (section)

==Examples==
* In [[chemistry]], compositions can be expressed as [[molar concentration]]s of each component. As the sum of all concentrations is not determined, the whole composition of ''D'' parts is needed and thus expressed as a vector of ''D'' molar concentrations. These compositions can be translated into weight per cent multiplying each component by the appropriated constant.
* In [[demography]], a town may be a compositional data point in a sample of towns; a town in which 35% of the people are Christians, 55% are Muslims, 6% are Jews, and the remaining 4% are others would correspond to the quadruple [0.35,&nbsp;0.55,&nbsp;0.06,&nbsp;0.04]. A data set would correspond to a list of towns.
* In [[geology]], a rock composed of different minerals may be a compositional data point in a sample of rocks; a rock of which 10% is the first mineral, 30% is the second, and the remaining 60% is the third would correspond to the triple [0.1,&nbsp;0.3,&nbsp;0.6]. A [[data set]] would contain one such triple for each rock in a sample of rocks.
* In [[DNA sequencing#High-throughput methods|high throughput sequencing]], data obtained are typically transformed to relative abundances, rendering them compositional. 
* In [[probability]] and [[statistics]], a partition of the sampling space into disjoint events is described by the probabilities assigned to such events. The vector of ''D'' probabilities can be considered as a composition of ''D'' parts. As they add to one, one probability can be suppressed and the composition is completely determined.
* In [[chemometrics]], for the classification of petroleum oils.<ref>{{cite journal | last1 = Olea | first1 = Ricardo A. | last2 = Martín-Fernández | first2 = Josep A. | last3 = Craddock | first3 = William H. | year = 2021 | title = Multivariate classification of the crude oil petroleum systems in southeast Texas, USA, using conventional and compositional analysis of biomarkers | journal = In Advances in Compositional Data Analysis—Festschrift in honor of Vera-Pawlowsky-Glahn, Filzmoser, P., Hron, K., Palarea-Albaladejo, J., Martín-Fernández, J.A., editors. Springer | pages = 303−327}}</ref>
* In a [[Survey (human research)|survey]], the proportions of people positively answering some different items can be expressed as percentages. As the total amount is identified as 100, the compositional vector of ''D'' components can be defined using only ''D''&nbsp;&minus;&nbsp;1 components, assuming that the remaining component is the percentage needed for the whole vector to add to 100.