what is the need of dummy variable and what are alternative to it
One-hot vs dummy encoding in Scikit-learn
How to clear bash history completely? What is the best Java email address validation method? What are the good email address validation libraries for Java?  Are there any alternatives to ? How do I test a private function or a class that has private methods, fields or inner classes? There has been a trend now two persons downvote it then it goes on like that. So let there be down voting but do not display the downvotes till the user votes on it. Else the user reads it with an impression that the question is not good.  Am I missing something? No CUDA and GPU option Let $X$ be an infinite cofinite space and let $A \subset X$ be infinite. Then $\overline A = X$  I am having a tough time in trying to understand this. Why is every infinite set in an infinite cofinite space dense ? Everytime I try to sudo something at the terminal, I get a warning message:  alexandre@XPS-15Z $ sudo mount file.iso /mnt/ -o loop [sudo] password for alexandre:  no talloc stackframe at ../source3/param/loadparm.c:4864, leaking memory   It's just annoying to get that all the time. How do I solve that? I'm on Ubuntu 14.04 (upgraded from 13.10) Note: If you're looking for a simple explanation as to why comments aren't required on downvotes, see .   I used to get "upset" (though that is too strong a term) when I got downvoted without comment. If my answer isn't good enough then I'd like to know why. Not only does it improve the answer for the OP but it improves my knowledge too.  Where the down-vote has been explained I've found it useful &amp; it has improved my answer, or forced me to delete the answer if it was totally wrong.  So is there any way we can encourage people to leave a comment? Perhaps they don't lose rep if they explain their down-vote?  I must admit though that I haven't always explained my down-vote either so you could call me a hypocrite. I've also grown a thicker skin over the months of using SO (it seems to have come with the higher rep score ;-)), so I'm less bothered about this now. I'm mainly a C# developer, but I'm currently working on a project in Python.  How can I represent the equivalent of an Enum in Python? Why are local variables not initialized in Java? I simply can't figure out what the capacity of this circuit is.  I can do the math myself, I just need a hint how to create an equivalent circuit where it is obvious what is parallel and what is in series... What happens to folks who get question banned, by and large? There is a steady stream of duplicates of  coming in lately. It's got me wondering. Roughly speaking, out of say 100 folks who get this ban, how many    wander away and never interact with SO again?   do the sorts of things that might lift a ban, but don't get it lifted? do the sorts of things they should, and lift the ban? post a question of their own on Meta which we close as a dupe?   Among the continue-to-interact folks, is there a difference in success rate between those who post on Meta about it (motivated, but not good rules-readers, who nonetheless get customized advice) and those who do not (better rules readers, but working to some extent blind) - which do better?  Is there a reasonable chance of recovering from a ban, assuming you care enough to try? How to make a standalone document with one equation? Test coverage for setCookies method I am adding cookie to my page in the controller using  ApexPages.currentPage().setCookies(new Cookie[]{CookieName});  When am trying to get the code coverage, my test class is not covering the above line.  How to get the code coverage for the above setcookie method in the test class. I need to run something as sudo without a password, so I used visudo and added this to my sudoers file:  MYUSERNAME ALL = NOPASSWD: /path/to/my/program   Then I tried it out:  $ sudo /path/to/my/program [sudo] password for MYUSERNAME:    Why does it ask for a password? How can I run/use commands as root with a non-root user, without asking for a password? Lazy Method for Reading Big File in Python? I have a very big file 4GB and when I try to read it my computer hangs. So I want to read it piece by piece and after processing each piece store the processed piece into another file and read next piece.  Is there any method to yield these pieces ?  I would love to have a lazy method. Is it possible to dual boot two OS's at the same time? Solution for A/C Condensate Drain Line that doesn't require emptying a bucket of water every day? Incompatibility between TikZ and babel So I installed vlc daily built snap package. It's working great, no problems there. However I noticed that after upgrade the system has 2 versions of vlc (7 and 9). That can be seen when browsing /snap/vlc/ directory and using system monitor. This is also the case with other snaps. Is there a way to automatically delete older versions of snaps? Or do I just delete them using plain &quot;rm&quot; command? Is it safe to delete them that way?