---
title: vendiscore
datasets:
-  
tags:
- evaluate
- metric
description: "The Vendi Score is a metric for evaluating diversity in machine learning. See the project's README at https://github.com/vertaix/Vendi-Score for more information."
sdk: gradio
sdk_version: 3.0.2
app_file: app.py
pinned: false
---

# Metric Card for VendiScore

The Vendi Score (VS) is a metric for evaluating diversity in machine learning.
The input to metric is a collection of samples and a pairwise similarity function, and the output is a number, which can be interpreted as the effective number of unique elements in the sample.
See the project's README at https://github.com/vertaix/Vendi-Score for more information.

## Metric Description
The Vendi Score (VS) is a metric for evaluating diversity in machine learning.
The input to metric is a collection of samples and a pairwise similarity function, and the output is a number, which can be interpreted as the effective number of unique elements in the sample.
Specifically, given an `n x n` positive semi-definite matrix `K` of similarity scores, the score is defined as:
```
VS(K) = exp(tr(K/n @ log(K/n))) = exp(-sum_i lambda_i log lambda_i),
```
where `lambda_i` are the eigenvalues of `K/n` and `0 log 0 = 0`.
That is, the Vendi Score is equal to the exponential of the von Neumann entropy of `K/n`, or the Shannon entropy of the eigenvalues, which is also known as the effective rank.

For more information, please see our paper, [The Vendi Score: A Diversity Evaluation Metric for Machine Learning](https://arxiv.org/abs/2210.02410).

## How to Use
The Vendi Score is available as a Python package or in HuggingFace `evaluate`.
To use the Python package, see the instructions at https://github.com/vertaix/Vendi-Score.
The `evaluate` module supports text, numbers, and precomputed similarity scores or feature embeddings.
Please use the Python package for more support for images and other datatypes.

To use the `evaluate` module, first install the requirements:
```
pip install evaluate
pip install vendi_score[all]
```
To calculate the score, pass a list of samples and a similarity function or a string identifying a predefined class of similarity functions (see below).
```
>>> vendiscore = evaluate.load("Vertaix/vendiscore", "text")
>>> sents = ["Look, Jane.", "See Spot.", "See Spot run.", "Run, Spot, run.", "Jane sees Spot run."]
>>> results = vendiscore.compute(samples=sents, k="ngram_overlap", ns=[1, 2])
>>> print(results)
{'VS': 3.90657...}
```

### Inputs
- **samples**: an iterable containing n samples to score; an n x n similarity
       matrix K, or an n x d feature matrix X.
- **k**: a pairwise similarity function, or a string identifying a predefined 
       similarity function. If k is a pairwise similarity function, it should
       be symmetric and k(x, x) = 1.
       Options: ngram_overlap, text_embeddings.
- **score_K**: if true, samples is an n x n similarity matrix K.
- **score_X**: if true, samples is an n x d feature matrix X.
- **score_dual**: if true,  samples is an n x d feature matrix X and we will
       compute the diversity score using the covariance matrix X @ X.T.
- **normalize**: if true, normalize the similarity scores.
- **model (optional)**: if k is "text_embeddings", a model mapping sentences to
       embeddings (output should be an object with an attribute called
       `pooler_output` or `last_hidden_state`).
- **tokenizer (optional)**: if k is "text_embeddings" or "ngram_overlap", a
       tokenizer mapping strings to lists.
- **model_path (optional)**: if k is "text_embeddings", the name of a model on
       the HuggingFace hub.
- **ns (optional)**: if k is "ngram_overlap", the values of n to calculate.
- **batch_size (optional)**: batch size to use if k is "text_embedding".
- **device (optional)**: a string (e.g. "cuda", "cpu") or torch.device 
       identifying the device to use if k is "text_embedding".


### Output Values

The output is a dictionary with one key, "VS".
Given n samples, the value of the Vendi Score ranges between 1 and n, with higher numbers indicating that the sample is more diverse.

### Examples

```
>>> import numpy as np
>>> vendiscore = evaluate.load("Vertaix/vendiscore", "int")
>>> samples = [0, 0, 10, 10, 20, 20]
>>> k = lambda a, b: np.exp(-np.abs(a - b))
>>> vendiscore.compute(samples=samples, k=k)
{'VS': 2.9999...}
```

If you already have precomputed a similarity matrix:
```
>>> vendiscore = evaluate.load("Vertaix/vendiscore", "K")
>>> K = np.array([[1.0, 0.9, 0.0],
                  [0.9, 1.0, 0.0],
                  [0.0, 0.0, 1.0]])
>>> vendiscore.compute(samples=K, score_K=True)
{'VS': 2.1573...}
```

If your similarity function is a dot product between `n` normalized
`d`-dimensional embeddings `X`, and `d` < `n`, it is faster
to compute the Vendi Score using the covariance matrix, `X @ X.T`.
(If the rows of `X` are not normalized, set `normalize = True`.)
```
>>> vendiscore = evaluate.load("Vertaix/vendiscore", "X")
>>> X = np.array([[100, 0], [99, 1], [1, 99], [0, 100]])
>>> vendiscore.compute(samples=X, score_dual=True, normalize=True)
{'VS': 1.99989...}
```

Text similarity can be calculated using n-gram overlap or using inner products between embeddings from a neural network.
```
>>> vendiscore = evaluate.load("Vertaix/vendiscore", "text")
>>> sents = ["Look, Jane.", "See Spot.", "See Spot run.", "Run, Spot, run.", "Jane sees Spot run."]
>>> ngram_vs = vendiscore.compute(samples=sents, k="ngram_overlap", ns=[1, 2])["VS"]
>>> bert_vs = vendiscore.compute(samples=sents, k="text_embeddings", model_path="bert-base-uncased")["VS"]
>>> print(f"N-grams: {ngram_vs:.02f}, BERT: {bert_vs:.02f}")
N-grams: 3.91, BERT: 1.21
```

## Limitations and Bias
The Vendi Score depends on the choice of similarity function. Care should be taken to select a similarity function that reflects the features that are relevant for defining diversity in a given application.

## Citation
```bibtex
@article{friedman2022vendi,
  title={The Vendi Score: A Diversity Evaluation Metric for Machine Learning},
  author={Friedman, Dan and Dieng, Adji Bousso},
  journal={arXiv preprint arXiv:2210.02410},
  year={2022}
}
```