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# isundefined

Find undefined elements in categorical array

## Syntax

``TF = isundefined(A)``

## Description

example

````TF = isundefined(A)` returns a logical array, `TF`, that indicates which elements in the categorical array, `A`, contain undefined values. `isundefined` returns logical `1` (`true`) for undefined elements; otherwise it returns logical `0` (`false`). The size of `TF` is the same as the size of `A`.Any elements in `A` without a corresponding category are undefined. Undefined values are similar to `NaN` in numeric arrays.```

## Examples

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Create a categorical array, `A`, from numeric values where `1`, `2`, and `3` represent red, green, and blue respectively.

`A = categorical([4 1; 2 3; 2 1; 3 4; 1 1],1:3,{'red','green','blue'})`
```A = 5x2 categorical array <undefined> red green blue green red blue <undefined> red red ```

`A` is a 5-by-2 categorical array with three categories: `red`, `green`, and `blue`. Array elements corresponding to the numeric value `4` in the input array to the `categorical` function do not have a corresponding category. Therefore, they are undefined in the output categorical array, `A`.

Find undefined elements in `A`.

`TF = isundefined(A)`
```TF = 5x2 logical array 1 0 0 0 0 0 0 1 0 0 ```

`A(1,1)` and `A(4,2)` are undefined.

## Input Arguments

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