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# isundefined

Find undefined elements in categorical array

## 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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### Categorical Array with Undefined Values

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 =

<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 =

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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### A — Categorical arrayvector | matrix | multidimensional array

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