Types of Machine Learning
Last updated
Last updated
There are various ways to classify machine learning algorithms. The most common classification of machine learning algorithms is based on their learning tasks and the problem(s) that they are solving. Figure XX shows the differences between various machine learning algorithms. In general, there are four types of machine learning algorithms, including supervised, unsupervised, semi-supervised, and reinforced learning. The following discusses each type of ML algorithm.
Figure XX – Machine learning types (source:)
Machine learning is usually divided into the following types:
Supervised learning aims to predict the value of an output from input measures given a set of input-output pairs. Put in more familiar terms, it is learning to map from inputs x to outputs y, given a set of input-output pairs (x, y). In order for this to be feasible, the data must be labeled: i.e., the input data (x) used to train the computer must have an outcome variable y for each case.
Unsupervised learning is applied when the data are unlabeled. In this case, we only have input data x and the goal is to find some interesting or underlying patterns in the data by which they may be grouped or clustered. Because labeling data is typically expensive to do, most data are unlabeled. Hence, unsupervised learning is highly important.
Reinforcement learning approach is used to learn how to act or behave in an environment where the only information available in the training process is “success” or “failure” (for example, training a robot to navigate).
Supervised learning – which sometimes goes under the rubric predictive analytics – can be further subdivided into areas:
Classification. In this case, the y value takes on discrete values, or classes. Mode choice, crash severity, vehicle identification are common examples of classification tasks in transportation.
Regression. Here, the y value can take on a continuous range of values, for example, traffic flow or travel time.