php-ml/docs/machine-learning/classification/k-nearest-neighbors.md
David Monllaó c1b1a5d6ac Support for multiple training datasets (#38)
* Multiple training data sets allowed

* Tests with multiple training data sets

* Updating docs according to #38

Documenting all models which predictions will be based on all
training data provided.

Some models already supported multiple training data sets.
2017-02-01 19:06:38 +01:00

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# KNearestNeighbors Classifier
Classifier implementing the k-nearest neighbors algorithm.
## Constructor Parameters
* $k - number of nearest neighbors to scan (default: 3)
* $distanceMetric - Distance object, default Euclidean (see [distance documentation](../../math/distance.md))
```
$classifier = new KNearestNeighbors($k=4);
$classifier = new KNearestNeighbors($k=3, new Minkowski($lambda=4));
```
## Train
To train a classifier simply provide train samples and labels (as `array`). Example:
```
$samples = [[1, 3], [1, 4], [2, 4], [3, 1], [4, 1], [4, 2]];
$labels = ['a', 'a', 'a', 'b', 'b', 'b'];
$classifier = new KNearestNeighbors();
$classifier->train($samples, $labels);
```
You can train the classifier using multiple data sets, predictions will be based on all the training data.
## Predict
To predict sample label use `predict` method. You can provide one sample or array of samples:
```
$classifier->predict([3, 2]);
// return 'b'
$classifier->predict([[3, 2], [1, 5]]);
// return ['b', 'a']
```