# cat

Concatenate arrays

## Syntax

``C = cat(dim,A,B)``
``C = cat(dim,A1,A2,…,An)``

## Description

example

````C = cat(dim,A,B)` concatenates `B` to the end of `A` along dimension `dim` when `A` and `B` have compatible sizes (the lengths of the dimensions match except for the operating dimension `dim`).```

example

````C = cat(dim,A1,A2,…,An)` concatenates `A1`, `A2`, … , `An` along dimension `dim`.You can use the square bracket operator `[]` to concatenate. For example, `[A,B]` or `[A B]` concatenates arrays `A` and `B` horizontally, and `[A; B]` concatenates them vertically.```

## Examples

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Create and concatenate two matrices vertically, then horizontally.

`A = ones(3)`
```A = 3×3 1 1 1 1 1 1 1 1 1 ```
`B = zeros(3)`
```B = 3×3 0 0 0 0 0 0 0 0 0 ```
`C1 = cat(1,A,B)`
```C1 = 6×3 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0 ```
`C2 = cat(2,A,B)`
```C2 = 3×6 1 1 1 0 0 0 1 1 1 0 0 0 1 1 1 0 0 0 ```

Create two 3-D arrays and concatenate them along the third dimension. The lengths of the first and second dimensions in the resulting array matches the corresponding lengths in the input arrays, while the third dimension expands.

```A = rand(2,3,4); B = rand(2,3,5); C = cat(3,A,B); szC = size(C)```
```szC = 1×3 2 3 9 ```

Create a table and add a row using a cell array.

```LastName = {'Sanchez';'Johnson';'Li';'Diaz'}; Age = [38;43;38;40]; T1 = table(LastName,Age)```
```T1=4×2 table LastName Age ___________ ___ {'Sanchez'} 38 {'Johnson'} 43 {'Li' } 38 {'Diaz' } 40 ```
```Trow = {'Brown',49}; T2 = cat(1,T1,Trow)```
```T2=5×2 table LastName Age ___________ ___ {'Sanchez'} 38 {'Johnson'} 43 {'Li' } 38 {'Diaz' } 40 {'Brown' } 49 ```

Concatenate a date character vector, a string date, and a datetime into a single column of dates. The result is a datetime vector.

```chardate = '2016-03-24'; strdate = "2016-04-19"; t = datetime('2016-05-10','InputFormat','yyyy-MM-dd'); C = cat(1,chardate,strdate,t)```
```C = 3x1 datetime 24-Mar-2016 19-Apr-2016 10-May-2016 ```

Create a cell array containing two matrices, and concatenate the matrices both vertically and horizontally.

```M1 = [1 2; 3 4]; M2 = [5 6; 7 8]; A1 = {M1,M2}; Cvert = cat(1,A1{:})```
```Cvert = 4×2 1 2 3 4 5 6 7 8 ```
`Chorz = cat(2,A1{:})`
```Chorz = 2×4 1 2 5 6 3 4 7 8 ```

## Input Arguments

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Dimension to operate along, specified as a positive integer scalar. For example, if `A` and `B` are both 2-by-2 matrices, then `cat(1,A,B)` concatenates vertically creating a 4-by-2 matrix. `cat(2,A,B)` concatenates horizontally creating a 2-by-4 matrix.

`dim` must be either 1 or 2 for table or timetable input.

First input, specified as a scalar, vector, matrix, multidimensional array, table, or timetable.

Second input, specified as a scalar, vector, matrix, multidimensional array, table, or timetable.

• The elements of `B` are concatenated to the end of the first input along the operating dimension. The sizes of the input arguments must be compatible. For example, if the first input is a matrix of size 3-by-2, then `B` must have 2 columns to concatenate vertically, and 3 rows to concatenate horizontally.

• When concatenating horizontally, all table inputs must have unique variable names. When present, row names must be identical, except for order. Similarly, all timetable inputs must have the same row times and all columns must have different names.

• You can concatenate valid combinations of different types. For more information, see Valid Combinations of Unlike Classes.

List of inputs, specified as a comma-separated list of arrays to concatenate in the order they are specified.

• The inputs must have compatible sizes. For example, if `A1` is a row vector of length m, then the remaining inputs must each have m columns to concatenate vertically.

• When concatenating horizontally, all table inputs must have unique variable names. When present, row names must be identical, except for order. Similarly, all timetable inputs must have the same row times and all columns must have different names.

• You can concatenate valid combinations of different types. For more information, see Valid Combinations of Unlike Classes.

## Tips

• To construct text by horizontally concatenating strings, character vectors, or cell arrays of character vectors, use the `strcat` function.

• To construct a single piece of delimited text from a cell array of character vectors or a string array, use the `strjoin` function.

## Algorithms

When concatenating an empty array to a nonempty array, `cat` omits the empty array in the output. For example, `cat(2,[1 2],[])` returns the row vector `[1 2]`.

If all input arguments are empty and have compatible sizes, then `cat` returns an empty array whose size is equal to the output size as when the inputs are nonempty. For example, `cat(2,zeros(0,1),zeros(0,2))` returns a 0-by-3 empty array.