# countcats

Count occurrences of categorical array elements by category

## Description

`B = countcats(`

returns
the number of elements in each category of the categorical array, `A`

)`A`

.

If

`A`

is a vector, then`countcats`

returns the number of elements in each category.If

`A`

is a matrix, then`countcats`

treats the columns of`A`

as vectors and returns the category counts for each column of`A`

.If

`A`

is a multidimensional array, then`countcats`

acts along the first array dimension whose size does not equal`1`

.

## Examples

### Category Counts of Categorical Vector

Create a 1-by-5 categorical vector.

A = categorical({'plane' 'car' 'train' 'car' 'plane'})

`A = `*1x5 categorical*
plane car train car plane

`A`

has three categories. To list the categories and their order, use the `categories`

function. Every element of `A`

belongs to one of the categories listed by the call to `categories`

.

categories(A)

`ans = `*3x1 cell*
{'car' }
{'plane'}
{'train'}

Find the number of elements in each category of `A`

.

B = countcats(A)

`B = `*1×3*
2 2 1

The first element in `B`

corresponds to the first category of `A`

, which is `car`

. The second element in `B`

corresponds to the second category of `A`

, which is `plane`

. The third element of `B`

corresponds to the third category of `A`

, which is `train`

.

Since `A`

is a row vector, `countcats`

returns a row vector.

### Category Counts of Each Column in Array

Create a 3-by-2 categorical array, `A`

, from a numeric array.

valueset = 1:3; catnames = {'red' 'green' 'blue'}; A = categorical([1 3; 2 1; 3 1],valueset,catnames)

`A = `*3x2 categorical*
red blue
green red
blue red

`A`

has three categories, `red`

, `green`

, and `blue`

.

Find the category counts of each column in `A`

.

B = countcats(A)

`B = `*3×2*
1 2
1 0
1 1

The first row of `B`

corresponds to the first category of `A`

. The value, `red`

, occurs once in the first column of `A`

and twice in the second column.

The second row of `B`

corresponds to the second category of `A`

. The value, `green`

, occurs once in the first column of `A`

, and it does not occur in the second column.

The third row of `B`

corresponds to the third category of `A`

. The value, `blue`

, occurs once in the first column of `A`

and once in the second column.

### Category Counts of Each Row in Array

Create a 3-by-2 categorical array, `A`

, from a numeric array.

valueset = 1:3; catnames = {'red' 'green' 'blue'}; A = categorical([1 3; 2 1; 3 1],valueset,catnames)

`A = `*3x2 categorical*
red blue
green red
blue red

`A`

has three categories, `red`

, `green`

, and `blue`

.

Find the category counts of `A`

along the second dimension.

B = countcats(A,2)

`B = `*3×3*
1 0 1
1 1 0
1 0 1

The first column of `B`

corresponds to the first category of `A`

. The value, `red`

, occurs once in the first row of `A`

, once in the second row, and once in the third row.

The second column of `B`

corresponds to the second category of `A`

. The value, `green`

, occurs in only one element. It occurs in the second row of `A`

.

The third column of `B`

corresponds to the third category of `A`

. The value, `blue`

, occurs once in the first row of `A`

and once in the third row.

### Category Counts of Array Containing Undefined Elements

Create a 6-by-1 categorical array, `A`

, from a numeric array.

valueset = 1:3; catnames = {'red' 'green' 'blue'}; A = categorical([1;3;2;1;3;1],valueset,catnames)

`A = `*6x1 categorical*
red
blue
green
red
blue
red

Remove the `blue`

category.

`A = removecats(A,'blue')`

`A = `*6x1 categorical*
red
<undefined>
green
red
<undefined>
red

`A`

has two categories, `red`

and `green`

. Elements of `A`

that were from the `blue`

category are now undefined.

Find the number of elements in each category of `A`

.

B = countcats(A)

`B = `*2×1*
3
1

The first element in `B`

corresponds to the first category of `A`

. The value, `red`

, occurs three times in `A`

.

The second element in `B`

corresponds to the second category of `A`

. The value, `green`

, occurs once in `A`

.

`countcats`

does not return any information on undefined elements.

Use the `summary`

function to view the number of undefined elements in addition to the number of elements in each category of `A`

.

summary(A)

red 3 green 1 <undefined> 2

## Input Arguments

`A`

— Categorical array

vector | matrix | multidimensional array

Categorical array, specified as a vector, matrix, or multidimensional array.

`dim`

— Dimension to operate along

positive integer scalar

Dimension to operate along, specified as a positive integer scalar. If no value is specified, then the default is the first array dimension whose size does not equal 1.

Consider a two-dimensional categorical array, `A`

.

If `dim = 1`

, then `countcats(A,1)`

returns
the category counts for each column of `A`

.

If `dim = 2`

, then `countcats(A,2)`

returns
the category counts of each row of `A`

.

If `dim`

is greater than `ndims(A)`

,
then `countcats(A)`

returns an array the same size
as `A`

for each category. `countcats`

returns `1`

for
elements in the corresponding category and `0`

otherwise.

## Tips

To find the number of undefined elements in a categorical array,

`A`

, you must use`summary`

or`isundefined`

.

## Extended Capabilities

### Tall Arrays

Calculate with arrays that have more rows than fit in memory.

This function fully supports tall arrays. For more information, see Tall Arrays.

### C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

### Thread-Based Environment

Run code in the background using MATLAB® `backgroundPool`

or accelerate code with Parallel Computing Toolbox™ `ThreadPool`

.

This function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

### Distributed Arrays

Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

This function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

## See Also

`iscategory`

| `ismember`

| `summary`

| `isundefined`

| `categories`

**Introduced in R2013b**

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