# reordercats

Reorder categories in `categorical` array

## Syntax

``B = reordercats(A)``
``B = reordercats(A,neworder)``

## Description

example

````B = reordercats(A)` reorders the categories in the `categorical` array, `A`, to be in alphanumeric order.The order of the categories is used by functions such as `summary` and `histogram`. If the `categorical` array is ordinal, the order of the categories defines their mathematical ordering. The first category specified is the smallest and the last category is the largest.```

example

````B = reordercats(A,neworder)` puts the categories in the order specified by `neworder`.```

## Examples

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Create two categorical arrays, `X` and `Y`.

`X = categorical({'frog';'cat';'cat';'ant';'frog'})`
```X = 5x1 categorical frog cat cat ant frog ```
`Y = categorical({'deer';'bear';'eagle';'deer'})`
```Y = 4x1 categorical deer bear eagle deer ```

`X` is a 5-by-1 categorical array. The categories of `X` are the sorted unique values from the array: `{'ant';'cat';'frog'}`.

`Y` is a 4-by-1 categorical array. The categories of `Y` are the sorted unique values from the array: `{'bear';'deer';'eagle'}`.

Concatenate `X` and `Y` into a single categorical array, `A`.

`A = [X;Y]`
```A = 9x1 categorical frog cat cat ant frog deer bear eagle deer ```

`vertcat` appends the values from `Y` to the values from `X`.

List the categories of the categorical array, `A`.

`acats = categories(A)`
```acats = 6x1 cell {'ant' } {'cat' } {'frog' } {'bear' } {'deer' } {'eagle'} ```

`vertcat` appends the categories of `Y` to the categories from `X`. The categories of `A` are not in alphabetical order.

Reorder the categories of `A` into alphabetical order.

`B = reordercats(A)`
```B = 9x1 categorical frog cat cat ant frog deer bear eagle deer ```

The output categorical array, `B`, has the same elements in the same order as the input categorical array, `A`.

List the categories of the categorical array, `B`.

`bcats = categories(B)`
```bcats = 6x1 cell {'ant' } {'bear' } {'cat' } {'deer' } {'eagle'} {'frog' } ```

The categories of `B` are in alphabetical order.

Create a categorical array containing the color of various items.

`A = categorical({'red';'green';'blue';'red';'green';'red';'blue';'blue'})`
```A = 8x1 categorical red green blue red green red blue blue ```

`A` is an 8-by-1 categorical array.

Display the categories of `A`.

`categories(A)`
```ans = 3x1 cell {'blue' } {'green'} {'red' } ```

The categories of `A` are in alphabetical order and have no mathematical meaning.

Reorder the categories to match the order commonly used for colors.

`B = reordercats(A,{'red','green','blue'})`
```B = 8x1 categorical red green blue red green red blue blue ```

`B` contains the same values as `A`.

Display the categories of `B`.

`categories(B)`
```ans = 3x1 cell {'red' } {'green'} {'blue' } ```

`B` is not ordinal and the order of the categories has no mathematical meaning. Although the categories appear in the order of the color spectrum, relational operations, such as greater than and less than, have no meaning.

Create an ordinal categorical array, `A`, containing modes of transportation. Order the categories based on the average price of travel.

```A = categorical({'plane';'car'; 'train';'car';'plane';'car'},... {'car','train','plane'},'Ordinal',true)```
```A = 6x1 categorical plane car train car plane car ```

`A` is a 6-by-1 ordinal categorical array.

Display the categories of `A`.

`categories(A)`
```ans = 3x1 cell {'car' } {'train'} {'plane'} ```

Since `A` is ordinal, `car < train < plane`.

Reorder the categories to reflect a decrease in the cost of train travel.

`B = reordercats(A,{'train','car','plane'})`
```B = 6x1 categorical plane car train car plane car ```

`B` contains the same values as `A`.

Display the categories of `B`.

`categories(B)`
```ans = 3x1 cell {'train'} {'car' } {'plane'} ```

The mathematical ordering of the categories is now `train < car < plane`. The results from relational operations, `min`, and `max` reflect the new category ordering.

Create a categorical array, `A`, containing modes of transportation.

`A = categorical({'plane';'car';'train';'car';'car';'plane';'car'})`
```A = 7x1 categorical plane car train car car plane car ```

Display the categories of `A`.

`categories(A)`
```ans = 3x1 cell {'car' } {'plane'} {'train'} ```

Reorder categories from least to most frequent occurrence in `A`.

```B = countcats(A); [C,neworder] = sort(B); neworder```
```neworder = 3×1 3 2 1 ```
```D = reordercats(A,neworder); categories(D)```
```ans = 3x1 cell {'train'} {'plane'} {'car' } ```

Because `countcats` counts the occurrences of each category, `neworder` describes how to reorder the categories—not the elements—of `A`.

Create a `categorical` array. This array has many different categories that stand for "yes" and "no".

`C = categorical(["Y" "Yes" "Yeah" "N" "No" "Nope"])`
```C = 1x6 categorical Y Yes Yeah N No Nope ```

List the categories in order. By default, the sort order of these categories is alphabetical order, because MATLAB® stores characters as Unicode®.

`categories(C)`
```ans = 6x1 cell {'N' } {'No' } {'Nope'} {'Y' } {'Yeah'} {'Yes' } ```

You can match multiple category names by using a `pattern`. For example, to specify category names that start with a `Y`, you can use a wildcard pattern. To create a wildcard pattern, use the `wildcardPattern` function.

Reorder the categories. Change the sort order so that the categories that start with `Y` come before the categories that start with `N`.

`C = reordercats(C,["Y"+wildcardPattern,"N"+wildcardPattern])`
```C = 1x6 categorical Y Yes Yeah N No Nope ```

List the categories in their new order.

`categories(C)`
```ans = 6x1 cell {'Y' } {'Yeah'} {'Yes' } {'N' } {'No' } {'Nope'} ```

## Input Arguments

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Input array, specified as a `categorical` array. If `A` is an ordinal `categorical` array, a reordering of the categories changes the mathematical meaning. Consequently, the relational operators, such as greater than and less than, might return different results.

New category order for `B`, specified as a string array, cell array of character vectors, numeric vector, or `pattern` array. `neworder` must be a permutation of `categories(A)`.

## Tips

• To convert the categorical array, `B`, to an ordinal categorical array, use `B = categorical(B,'Ordinal',true)`. You can specify the order of the categories with `B = categorical(B,valueset,'Ordinal',true)`, where the order of the values in `valueset` defines the category order.

## Version History

Introduced in R2013b