How much can you earn as a freelancer?

I’m always interested in freelancing and wonder how freelancers can earn money from the clients, specifically, I want to know what kinds of jobs are most posted, what skills do the clients need and how much do freelancers usually earn. Bear these questions in my mind, I explored the data of job posts on Upwork and had some interesting discoveries.
Below is the process how I explored written in Ipython notebook.
Before the analysis above, I thought the Data Science jobs were all about machine learning, algorithms, etc. , but it turns out that the market doesn’t think so. The clients who pay you may believe that skills like data analysis, web scraping are also if not more crucial to their business. Job seekers in data science may need to adjust their expectations to prepare themselves with skills like data analysis and web scraping besides machine learning.