Changing research field as PhD applicant I am a CS undergrad currently thinking about my post grad application. I have a couple of questions. 

So far, I published 2 first author papers, one in SODA, and one in VLDB. However, they're on two totally different topics (One on compression algorithms [theory], one on graphs [DB related])

I recently (last year) started getting interested in Machine Learning and specifically reinforcement learning, and have been spending a whole lot of time on it. I decided I want to apply to a PhD in that field. 

Would my unrelated previous research papers add any positive thing to my application, or would it just be better to apply to a PhD that relates to my my published papers?
Would my unrelated previous research papers add any positive thing to
  my application [...]?


Your past research will certainly strengthen your application, even if it's not in the subfield you aspire to study in graduate school. Grad schools look for students interested in and able to carry out research, and a lot of those skills are transferable across disciplines and certainly subfields. It's also perfectly normal to change your research interests during undergrad (or be constrained in topic choice by what faculty in your department are working on or any other number of factors).


  [...] would it just be better to apply to a PhD that relates to my my
  published papers?


With the caveat that you should feel sufficiently committed to your new field to not lose interest in grad school, you should definitely want to apply for the PhD that you want to do rather than the PhD you think your CV makes you look like the best candidate for. You'll be in a program that better matches your interests and you'll do work that's more meaningful to you (and hence often much better).