# Documentation

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# eq, ==

Determine equality

## Syntax

• ``A == B``
example
• ``eq(A,B)``

## Description

example

````A == B` returns a logical array with elements set to logical `1` (`true`) where arrays `A` and `B` are equal; otherwise, the element is logical `0` (`false`). The test compares both real and imaginary parts of numeric arrays. `eq` returns logical `0` (`false`) where `A` or `B` have NaN or undefined categorical elements.```
````eq(A,B)` is an alternative way to execute `A == B`, but is rarely used. It enables operator overloading for classes.```

## Examples

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Create two vectors containing both real and imaginary numbers, then compare the vectors for equality.

```A = [1+i 3 2 4+i]; B = [1 3+i 2 4+i]; A == B ```
```ans = 1×4 logical array 0 0 1 1 ```

The `eq` function tests both real and imaginary parts for equality, and returns logical `1` (`true`) only where both parts are equal.

Create a character vector.

```M = 'masterpiece'; ```

Test for the presence of a specific character using `==`.

```M == 'e' ```
```ans = 1×11 logical array 0 0 0 0 1 0 0 0 1 0 1 ```

The value of logical `1` (`true`) indicates the presence of the character `'e'`.

Create a categorical array with two values: `'heads'` and `'tails'`.

```A = categorical({'heads' 'heads' 'tails'; 'tails' 'heads' 'tails'}) ```
```A = heads heads tails tails heads tails ```

Find all values in the `'heads'` category.

```A == 'heads' ```
```ans = 2×3 logical array 1 1 0 0 1 0 ```

A value of logical `1` (`true`) indicates a value in the category.

Compare the rows of `A` for equality.

```A(1,:) == A(2,:) ```
```ans = 1×3 logical array 0 1 1 ```

A value of logical `1` (`true`) indicates where the rows have equal category values.

Many numbers expressed in decimal text cannot be represented exactly as binary floating numbers. This leads to small differences in results that the `==` operator reflects.

Perform a few subtraction operations on numbers expressed in decimal and store the result in `C`.

```C = 0.5-0.4-0.1 ```
```C = -2.7756e-17 ```

With exact decimal arithmetic, `C` should be equal to exactly `0`. Its small value is due to the nature of binary floating-point arithmetic.

Compare `C` to `0` for equality.

```C == 0 ```
```ans = logical 0 ```

Compare floating-point numbers using a tolerance, `tol`, instead of using `==`.

```tol = eps(0.5); abs(C-0) < tol ```
```ans = logical 1 ```

The two numbers, `C` and `0`, are closer to one another than two consecutive floating-point numbers near `0.5`. In many situations, `C` may act like `0`.

Compare the elements of two `datetime` arrays.

Create two `datetime` arrays in different time zones.

```t1 = [2014,04,14,9,0,0;2014,04,14,10,0,0]; A = datetime(t1,'TimeZone','America/Los_Angeles'); A.Format = 'd-MMM-y HH:mm:ss Z' ```
```A = 2×1 datetime array 14-Apr-2014 09:00:00 -0700 14-Apr-2014 10:00:00 -0700 ```
```t2 = [2014,04,14,12,0,0;2014,04,14,12,30,0]; B = datetime(t2,'TimeZone','America/New_York'); B.Format = 'd-MMM-y HH:mm:ss Z' ```
```B = 2×1 datetime array 14-Apr-2014 12:00:00 -0400 14-Apr-2014 12:30:00 -0400 ```

Check where elements in `A` and `B` are equal.

```A==B ```
```ans = 2×1 logical array 1 0 ```

## Input Arguments

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Left array, specified as a scalar, vector, matrix, or multidimensional array. Numeric or string inputs `A` and `B` must either be the same size or have sizes that are compatible (for example, `A` is an `M`-by-`N` matrix and `B` is a scalar or `1`-by-`N` row vector). For more information, see Compatible Array Sizes for Basic Operations.

If `A` and `B` are categorical, datetime, or duration arrays, then they must be the same size unless one is a scalar.

• If one input is a categorical array, the other input can be a categorical array, a cell array of character vectors, or a single character vector. A single character vector expands into a cell array of character vectors of the same size as the other input. If both inputs are ordinal categorical arrays, they must have the same sets of categories, including their order. If both inputs are categorical arrays that are not ordinal, they can have different sets of categories. See Compare Categorical Array Elements for more details.

• If one input is a datetime array, the other input can be a datetime array, a character vector, or a cell array of character vectors.

• If one input is a duration array, the other input can be a duration array or a numeric array. The operator treats each numeric value as a number of standard 24-hour days.

• If one input is a string array, the other input can be a string array, a character vector, or a cell array of character vectors. The corresponding elements of `A` and `B` are compared lexicographically.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `logical` | `char` | `string` | `categorical` | `datetime` | `duration`
Complex Number Support: Yes

Right array, specified as a scalar, vector, matrix, or multidimensional array. Numeric or string inputs `A` and `B` must either be the same size or have sizes that are compatible (for example, `A` is an `M`-by-`N` matrix and `B` is a scalar or `1`-by-`N` row vector). For more information, see Compatible Array Sizes for Basic Operations.

If `A` and `B` are categorical, datetime, or duration arrays, then they must be the same size unless one is a scalar.

• If one input is a categorical array, the other input can be a categorical array, a cell array of character vectors, or a single character vector. A single character vector expands into a cell array of character vectors of the same size as the other input. If both inputs are ordinal categorical arrays, they must have the same sets of categories, including their order. If both inputs are categorical arrays that are not ordinal, they can have different sets of categories. See Compare Categorical Array Elements for more details.

• If one input is a datetime array, the other input can be a datetime array, a character vector, or a cell array of character vectors.

• If one input is a duration array, the other input can be a duration array or a numeric array. The operator treats each numeric value as a number of standard 24-hour days.

• If one input is a string array, the other input can be a string array, a character vector, or a cell array of character vectors. The corresponding elements of `A` and `B` are compared lexicographically.

Data Types: `single` | `double` | `int8` | `int16` | `int32` | `int64` | `uint8` | `uint16` | `uint32` | `uint64` | `logical` | `char` | `string` | `categorical` | `datetime` | `duration`
Complex Number Support: Yes

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### Tall Array Support

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

### Tips

• When comparing handle objects, use `==` to test whether objects have the same handle. Use `isequal` to determine if objects with different handles have equal property values.