## Documentation Center |

The `nominal` and `ordinal` array
data types might be removed in a future release. To represent ordered
and unordered discrete, nonnumeric data, use the MATLAB^{®} `categorical` data type instead.

`C = union(A,B)[C,IA,IB] = union(A,B)[...] = union(A,B,'rows')[...] = union(...,'legacy')[...] = union(A,B,setOrder)[...]
= union(A,B,'rows',setOrder)`

`C = union(A,B)` for categorical vectors `A` and `B`,
returns a categorical vector `C` containing the combined
values from `A` and `B` with no
repetitions. The result `C` is sorted. The set of
categorical levels for `C` is the sorted union of
the sets of levels of the inputs, as determined by their labels.

`[C,IA,IB] = union(A,B)` also returns index
vectors `IA` and `IB` such that `C` is
a sorted combination of the elements `A(IA)` and `B(IB)`.
If there are common values in `A` and `B`,
then the index is returned in `IB`. If there are
repeated values in `A` or `B`, then
the index of the last occurrence of each repeated value is returned.

`[...] = union(A,B,'rows')` for categorical
matrices `A` and `B` with the same
number of columns, returns the combined rows from the two matrices
with no repetitions. The rows of the matrix `C` are
sorted. The set of categorical levels for `C` is
the sorted union of the sets of levels of the inputs. The optional
outputs `IA` and `IB` are index
vectors such that `C` is the sorted combination of
the rows `C = A(IA,:)` and `C = B(IB,:)`.

`[...] = union(...,'legacy')` preserves the
pre-2012a behavior of `union`. You can specify the
flag as the final argument with any previous syntax that accepts `A`, `B`,
or `'rows'`.

`[...] = union(A,B,setOrder)` and `[...]
= union(A,B,'rows',setOrder)` returns the observations of `C` in
a specific order. `setOrder='sorted'` returns the
values or rows of `C` in sorted order. `setOrder='stable'` returns
the values or rows of `C` in the same order as `A`,
then `B`. If `A` and `B` are
row vectors, then `C` is also a row vector. Otherwise, `C` is
a column vector. `IA` and `IB` are
column vectors. If there are repeated common values in `A` or `B`,
then the index of the first occurrence of each repeated value is returned.

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