php-ml/docs/machine-learning/preprocessing/normalization.md

# Normalization

Normalization is the process of scaling individual samples to have unit norm.

## L2 norm

[http://mathworld.wolfram.com/L2-Norm.html](http://mathworld.wolfram.com/L2-Norm.html)

Example:

```
use Phpml\Preprocessing\Normalizer;

$samples = [
    [1, -1, 2],
    [2, 0, 0],
    [0, 1, -1],
];

$normalizer = new Normalizer();
$normalizer->preprocess($samples);

/*
$samples = [
  [0.4, -0.4, 0.81],
  [1.0, 0.0, 0.0],
  [0.0, 0.7, -0.7],
];
*/

```

## L1 norm

[http://mathworld.wolfram.com/L1-Norm.html](http://mathworld.wolfram.com/L1-Norm.html)

Example:

```
use Phpml\Preprocessing\Normalizer;

$samples = [
    [1, -1, 2],
    [2, 0, 0],
    [0, 1, -1],
];

$normalizer = new Normalizer(Normalizer::NORM_L1);
$normalizer->preprocess($samples);

/*
$samples = [
   [0.25, -0.25, 0.5],
   [1.0, 0.0, 0.0],
   [0.0, 0.5, -0.5],
];
*/

```