I know what is Probability Density Function and its application in Machine Learning and Statistics. The problem I faced is that how does it being calculated? For a specific example like the probability of amount of rain in a rainy day, the researchers measure the rain amount for specific period of time and they make a function for that (frequentist approach)?
More specifically, The question is about how the following diagram is obtained?
PS It's not related to this question, because I asked how to create a diagram like the following diagram!