List comprehensions is a elegant way of making lists with one line of code. Consider the following example

Output

The format of list comprehension follows the format

Below is a more complex example

A lambda function is a anonymous function which can only have one expression. 

Basic definition

A lambda function that takes three argument a, b, c and multiply them can be written as

Principal component analysis is popular method to reduce high dimension data.

Let \(X_{i}=(x_{1i},x_{2i},...,x_{K,i}) ^{'}\) be a k-dimension vector for each  \(i=1,2,...,N\).