# shiftdata

Shift data to operate on specified dimension

## Syntax

`[x,perm,nshifts] = shiftdata(x,dim)`

## Description

`[x,perm,nshifts] = shiftdata(x,dim)` shifts data `x` to permute dimension `dim` to the first column using the same permutation as the built-in `filter` function. The vector `perm` returns the permutation vector that is used.

If `dim` is missing or empty, then the first nonsingleton dimension is shifted to the first column, and the number of shifts is returned in `nshifts`.

`shiftdata` is meant to be used in tandem with `unshiftdata`, which shifts the data back to its original shape. These functions are useful for creating functions that work along a certain dimension, like `filter`, `goertzel`, `sgolayfilt`, and `sosfilt`.

## Examples

collapse all

### Permute Dimensions of a Magic Square

This example shifts `x`, a 3-by-3 magic square, permuting dimension 2 to the first column. `unshiftdata` shifts `x` back to its original shape.

Create a 3-by-3 magic square.

```x = magic(3) ```
```x = 8 1 6 3 5 7 4 9 2 ```

Shift the matrix `x` to work along the second dimension. The permutation vector, `perm`, and the number of shifts, `nshifts`, are returned along with the shifted matrix.

```[x,perm,nshifts] = shiftdata(x,2) ```
```x = 8 3 4 1 5 9 6 7 2 perm = 2 1 nshifts = [] ```

Shift the matrix back to its original shape.

```y = unshiftdata(x,perm,nshifts) ```
```y = 8 1 6 3 5 7 4 9 2 ```

### Rearrange Array to Operate on First Nonsigleton Dimension

This example shows how `shiftdata` and `unshiftdata` work when you define `dim` as empty.

Define `x` as a row vector.

```x = 1:5 ```
```x = 1 2 3 4 5 ```

Define `dim` as empty to shift the first non-singleton dimension of `x` to the first column. `shiftdata` returns `x` as a column vector, along with `perm`, the permutation vector, and `nshifts`, the number of shifts.

```[x,perm,nshifts] = shiftdata(x,[]) ```
```x = 1 2 3 4 5 perm = [] nshifts = 1 ```

Using `unshiftdata`, restore `x` to its original shape.

```y = unshiftdata(x,perm,nshifts) ```
```y = 1 2 3 4 5 ```