# partition

(definition)

**Definition:**
(1) A division of a *set* into nonempty *disjoint sets* that completely cover the set. (2) To rearrange the elements of an *array* into two (or more) groups, typically, such that elements in the first group are less than a value and elements in the second group are greater.

**Formal Definition:** (1) A partition P of a set S is a set of subsets with the following properties:

- ∀ s
_{i} ∈ P, s_{i} ≠ ø

(no subset is empty), - ∀ s
_{i}, s_{j} ∈ P, i ≠ j → s_{i} ∩ s_{j} = ø

(subsets are disjoint), and -
**U**_{i=1} s_{i} = S

(subsets exactly cover the original).

Thanks to Julio A. Cartaya <jac@puma.mt.att.com>.

**Generalization** (I am a kind of ...)

*set*.

**Specialization** (... is a kind of me.)

*select and partition*.

**Aggregate parent** (I am a part of or used in ...)

*quicksort*, *Dutch national flag*, *American flag sort*.

**See also**
*set packing*, *subset*, *connected components*.

Author: PEB

## Implementation

generating partitions (Fortran, Mathematica, Pascal, and C).

Go to the
Dictionary of Algorithms and Data
Structures home page.

If you have suggestions, corrections, or comments, please get in touch
with Paul Black.

Entry modified 2 March 2015.

HTML page formatted Mon Mar 2 16:13:48 2015.

Cite this as:

Paul E. Black, "partition", in
*Dictionary of Algorithms and Data Structures* [online], Vreda Pieterse and Paul E. Black, eds. 2 March 2015. (accessed TODAY)
Available from: http://www.nist.gov/dads/HTML/partition.html