Semi-supervised learning in Machine learning

Problems, where we have a large amount of input data and only some of the data, are labeled are called semi-supervised and unsupervised learning.

A good example is a photo archive where only some of the images are labeled, (e.g. dog, cat, person) and the majority are unlabeled. Many real-world machine learning problems fall into this area. This is because it can be expensive or time-consuming to label data as it may require access to domain experts. Whereas unlabeled data is cheap and easy to collect and store. 

We can use unsupervised learning techniques to discover and learn the structure in the input variables. We can also use supervised learning techniques to make a best-guess prediction for the unlabeled data, feed that data back into the supervised learning algorithm as training data, and use the model to make predictions on new unseen data.