php-ml/docs/machine-learning/feature-extraction/tf-idf-transformer.md
2016-07-12 00:21:34 +02:00

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# Tf-idf Transformer
Tfidf, short for term frequencyinverse document frequency, is a numerical statistic that is intended to reflect how important a word is to a document in a collection or corpus.
### Constructor Parameters
* $samples (array) - samples for fit tf-idf model
```
use Phpml\FeatureExtraction\TfIdfTransformer;
$samples = [
[1, 2, 4],
[0, 2, 1]
];
$transformer = new TfIdfTransformer($samples);
```
### Transformation
To transform a collection of text samples use `transform` method. Example:
```
use Phpml\FeatureExtraction\TfIdfTransformer;
$samples = [
[0 => 1, 1 => 1, 2 => 2, 3 => 1, 4 => 0, 5 => 0],
[0 => 1, 1 => 1, 2 => 0, 3 => 0, 4 => 2, 5 => 3],
];
$transformer = new TfIdfTransformer($samples);
$transformer->transform($samples);
/*
$samples = [
[0 => 0, 1 => 0, 2 => 0.602, 3 => 0.301, 4 => 0, 5 => 0],
[0 => 0, 1 => 0, 2 => 0, 3 => 0, 4 => 0.602, 5 => 0.903],
];
*/
```