\textcolor{pink}{\huge \textsf{WELCOME! ^-^}}
@shadeless
Take the time to check out the FAQ and GUIDE if you haven’t already.
There’s also a lot of good stuff on the forum to help you, like:
The Ultimate Guide for WK
The Ultimate Additional Japanese Resources List!
The New And Improved List Of API and Third Party Apps
I hope your Japanese learning journey goes well and that you enjoy your time with us on the forums.
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I’m not an expert on the subject I’m afraid, but a browse of /r/LearnJapanese has highlighted two projects that might help, though they’re both a little unmaintained by the looks of it, though that doesn’t neccesarily mean that they’re not good ^-^
nplusone Japanese Sentence Miner
cb’s Japanese Text Analysis Tool
Both of those look to be able to generate data on frequency and commonality.