# union

Class: dataset

(Not Recommended) Set union for dataset array observations

The `dataset` data type is not recommended. To work with heterogeneous data, use the MATLAB® `table` data type instead. See MATLAB `table` documentation for more information.

## Syntax

```C = union(A,B) C = union(A,B,vars) C = union(A,B,vars,setOrder) [C,iA,iB] = union(___) ```

## Description

`C = union(A,B)` for `dataset` arrays `A` and `B` returns the combined set of observations from the two arrays, with repetitions removed. The observations in the dataset array `C` are sorted.

`C = union(A,B,vars)` returns the combined set of observations from the two arrays, with repetitions of unique combinations of the variables specified in `vars` removed. The observations in the dataset array `C` are sorted by those variables.

The values for variables not specified in `vars` for each observation in `C` are taken from the corresponding observation in `A` or `B`, or from `A` if there are common observations in both `A` and `B`. If there are multiple observations in `A` or `B` that correspond to an observation in `C`, those values are taken from the first occurrence.

`C = union(A,B,vars,setOrder)` returns the observations in `C` in the order specified by `setOrder`.

```[C,iA,iB] = union(___)``` also returns index vectors `iA` and `iB` such that `C` is a sorted combination of the values `A(iA,:)` and `B(iB,:)`. If there are common observations in `A` and `B`, then `union` returns only the index from `A`, in `iA`. If there are repeated observations in `A` or `B`, then the index of the first occurrence is returned. You can use any of the previous input arguments.

## Input Arguments

`A,B`

Input dataset arrays.

`vars`

String array or cell array of character vectors containing variable names, or a vector of integers containing variable column numbers. `vars` indicates the variables for which `union` removes repetitions of unique combinations of the variables.

Specify `vars` as `[]` to use its default value of all variables.

`setOrder`

Flag indicating the sorting order for the observations in `C`. The possible values of `setOrder` are:

 `'sorted'` Observations in `C` are in sorted order (default). `'stable'` Observations in `C` are in the same order that they appear in `A`, then `B`.

## Output Arguments

 `C` Dataset array with the combined observations of `A` and `B`, with repetitions removed. `C` is in sorted order (by default), or the order specified by `setOrder`. `iA` Index vector, indicating the observations in `A` that contribute to the union. `iA` contains the index to the first occurrence of any repeated observations in `A`. `iB` Index vector, indicating the observations in `B` that contribute to the union. If there are common observations in `A` and `B`, then `union` returns only the index from `A`, in `iA`. `iB` contains the index to the first occurrence of any repeated observations in `B`.