> For the complete documentation index, see [llms.txt](https://vikram-bajaj.gitbook.io/cs-gy-6923-machine-learning/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://vikram-bajaj.gitbook.io/cs-gy-6923-machine-learning/main-4/types-of-machine-learning/unsupervised-learning.md).

# Unsupervised Learning

In this kind of learning, we do not have labeled training data.

The most common unsupervised problem is **clustering**. There are also other unsupervised problems such as dimensionality reduction.

Some applications of clustering include:

* color quantization (16 million colors to 256 colors)
* directed marketing (different ads for different groups of people)
* pre-processing stage in supervised learning (in certain cases where it is clear that the examples are coming from well-defined groups)