title: Cleaning survey data in python - how to finding and cleaning common rows in two files?
body: <p>I am working on a survey data analysing project which consist 2 Excel files- in file <strong>pre-survey</strong>, it contains 800+ response records; while in <strong>post-survey</strong> file it contains 500ish responses. Both of them have (at least) one common column SID (Student ID). Something <strong>Y</strong> happened in between, and I am interested analysing the effectiveness of Y, and in what degrade Y impacts on different categories of people.</p>
  
  <p>What adds more complexity is that in each Excel file, it contains multiple tabs. Different interviewers interviewed several interviewees and documented in each tabs for different sections of survey. Columns may or may not be the same for different tabs, so it would be hard to be complied in one file. (Or does it actually make sense to combine them in one with lots of null values?)</p>
  
  <p>I am trying to find the students who did both pre- and post- surveys. How can I do it across sheets and files using python/pandas/other packages?</p>
  
  <p>Bonus if you could also suggest the approach to solve the problem.</p>