Since the feature selection method may remove some correlated but informative features, you have to consider combining these correlated features into a single feature with the feature extraction method. PCA is one of the feature extraction methods that performs orthogonal transformation to convert possibly correlated variables into principal components. Also, you can use these principal components to identify the directions of variance.
The process of PCA involves the following steps: firstly, find the mean vector, 
where xi indicates the data point, and n denotes the number of points. Secondly, compute the covariance matrix ...
