title: How do I classify when I have only positive use case of data in machine learning?
body: <p>My question is Can we classify something when we have a set of data which is related to only positive use case of a data? </p>
  
  <p>I know this is confusing, let me put it this way, say.. </p>
  
  <p>In a classifier, we have to train it with A and B where A is the positive data set and B is the negative data set. But here I have only positive data set of my action/use case and have no way to retrieve negative data set. </p>
  
  <p>Can I use machine learning to classify whether the coming data is positive or not? </p>
  
  <p>If yes, which classifier can be used to get my job done? </p>
  
  <p>A ruby based solution is preferred. </p>
  
  <p>Thanks.</p>