title: How to Replace Nan Values Meaningfully for Machine Learning
body: <p>I have a few categorical variables which I binary encoded.</p>
  
  <p>The problem is there are a lot of Nan values, I know I can just do <code>df.fillna(0)</code> for replacing the nan values..but will that be meaningful for machine learning?</p>
  
  <p>Some columns have data and some columns are filled with Nans, and this varies row by row.</p>
  
  <p>How to make the data useful? What specific operation is required?</p>