title: Example for non-iid data
body: <p>I have read some papers regarding to <em>non-iid</em> data. Based on Wikipedia, I know what <em>iid</em> (independent and identical distributed) data is but am still confused about <em>non-iid</em>. I did some research but could not find a clear definition and example of it. Can someone help me on this?</p>