How to store data in matrix form from a for loop extracting data from a several sub directories?

I have main directory and many sub-directories inside it. Every sub directories have data files that I want to extract. I have read data of all sub directories using for loop but I want to store every data of each sub directory that I used in for loop in separate matrix form so that I can use that data for other purpose (like to find mean and median). Any help is highly appreciated.