title: How to convert postgres column type from string to float
body: <p>I have a rails app with a basic postgres db, but I realized that some of my columns are strings and it'd be best if they were floats. I'm trying to convert columns for latitude and longitude from varchar to floating-point.  </p>
  
  <p>I've tried this post <a href="https://stackoverflow.com/questions/10690289/rails-gmaps4rails-gem-on-postgres">Rails - gmaps4rails gem on postgres</a> but I kept getting this error, <code>ERROR:  invalid input syntax for type double precision: ""</code>.  I'm willing to try anything else, and I've seen solutions for ways to do it with postgres queries, but I'm uncertain of how to implement them.  It's a straightforward problem; "-73.88537758790638" I want to become -73.88537758790638.  I just can't seem to find a working solution or one that I understand how to implement.</p>