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# eq, ==

Determine equality

## Description

example

A == B returns a logical array with elements set to logical 1 (true) where arrays A and B are equal; otherwise, it returns 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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### Equality of Two Vectors

Create two vectors containing both real and imaginary numbers.

```A = [1+i 3 2 4+i];
B = [1 3+i 2 4+i];```

Compare the two vectors for equality.

`A == B`
```ans =

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.

### Find Characters in String

Create a string of characters.

`M = 'masterpiece';`

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

```M == 'e'
```
```ans =

0     0     0     0     1     0     0     0     1     0     1```

The value of logical 1 (true) in the vector indicates the presence of the character 'e' in the string.

### Find Values in Categorical Array

Create a categorical array.

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

The array has two categories: 'heads' and 'tails'.

Find all values in the 'heads' category.

`A == 'heads'`
```ans =

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 =

0     1     1```

The function returns logical 1 (true) where the rows have equal category values.

### Compare Floating-Point Numbers

Some floating-point numbers cannot be represented exactly in binary form. This leads to small differences in results that the == operator reflects.

Perform a few subtraction operations on a floating-point number and store the result in C.

```C = 0.5-0.4-0.1
```
```C =

-2.7756e-17
```

Intuitively, C should be equal to exactly 0. Its small value is due to the nature of floating-point arithmetic.

Compare C to zero for equality.

`C == 0`
```ans =

0```

The result is logical 0 (false).

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

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

1
```

The two numbers, C and 0, are closer to one another than two consecutive floating-point numbers. They are essentially equal.

### Compare Datetime Values

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 =

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 =

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 =

1
0

```

## Input Arguments

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### A — Left arraynumeric array | logical array | character array | categorical array | datetime array | duration array

Left array, specified as a numeric array, logical array, character array, categorical array, datetime array, or duration array. Inputs A and B must be the same size unless one is a scalar. A scalar input expands into an array of the same size as the other input.

If one input is a categorical array, the other input can be a categorical array, a cell array of strings, or a single string. A single string expands into a cell array of strings 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 date string, or a cell array of date strings.

If one input is a duration array, the other input can be a duration array or a numeric array. eq treats each numeric value as a number of standard (86400 s) days.

Complex Number Support: Yes

### B — Right arraynumeric array | logical array | character array | categorical array | datetime array | duration array

Right array, specified as a numeric array, logical array, character array, or categorical array. Inputs A and B must be the same size unless one is a scalar. A scalar input expands into an array of the same size as the other input.

If one input is a categorical array, the other input can be a categorical array, a cell array of strings, or a single string. A single string expands into a cell array of strings 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 date string, or a cell array of date strings.

If one input is a duration array, the other input can be a duration array or a numeric array. eq treats each numeric value as a number of standard (86400 s) days.

Complex Number Support: Yes