Candidate sampling

See also: Machine learning terms

Candidate Sampling in Machine Learning

Candidate sampling is a method used in machine learning, particularly in the context of training large-scale models. It is an optimization technique that reduces the computational complexity of learning algorithms by approximating the gradient of the loss function. In this section, we will explore the concept of candidate sampling, its motivation, and its applications in machine learning.

Motivation

In machine learning problems, particularly those involving classification tasks, the number of classes or categories can be extremely large. Training a model on a large number of classes often requires significant computational resources and time. Candidate sampling techniques aim to address this challenge by approximating the gradient of the loss function, which can lead to more efficient training processes.

Techniques

There are various candidate sampling techniques used in machine learning, including:

• Negative Sampling: In this method, a small number of negative examples are sampled from the entire dataset to approximate the gradient of the loss function. It is particularly popular in the context of word2vec models for learning word embeddings.

• Importance Sampling: Importance sampling involves approximating the gradient by re-weighting the sampled candidates according to their importance. The importance is determined by the ratio between the true probability distribution and the sampling distribution.

• Noise Contrastive Estimation (NCE): NCE is another candidate sampling technique that aims to distinguish between the true data distribution and an artificially generated noise distribution. It estimates the parameters of the model by maximizing the likelihood of the data under this distinction.

Applications

Candidate sampling techniques have been successfully applied in various machine learning tasks, such as:

• Natural Language Processing (NLP): Candidate sampling is widely used in the training of word embedding models, such as word2vec and GloVe. These models learn vector representations of words from large text corpora, and candidate sampling helps to reduce the computational complexity of the training process.

• Recommender Systems: In large-scale recommender systems, candidate sampling can be used to efficiently train models that predict user preferences, even when there are millions of items or users involved.

• Computer Vision: Candidate sampling has been employed in training deep learning models for object recognition, particularly when there are a large number of object classes.

Explain Like I'm 5 (ELI5)

Imagine you have a giant jar filled with different types of candy, and you want to learn what each type tastes like. Instead of trying every single candy in the jar, you decide to taste a small number of them, which is faster and easier. This is similar to what candidate sampling does in machine learning.

When training a machine learning model, there are often many categories or classes to learn about. Instead of using all the data, which can take a very long time, candidate sampling picks a smaller, more manageable group of examples to learn from. This makes the learning process faster and more efficient, so the model can still do a good job even without using all the data.