Both Python 2.7 and 3.6 are installed by default in Ubuntu 18. But I wish to use the Anaconda Python with conda package manager. To avoid any conflicts I wish to completely remo
Don't do that , just don't.
you'll have regrets a lot of it.
And I'm serious.
A lot of things will deleted,but by the way, if you already done that don't worry, there is a solutions.
Just run this code in your terminal
sudo apt install ubuntu-desktop
And if you want you can run this one too
#ubuntu-18.04.1
sudo apt install $( curl http://releases.ubuntu.com/18.04/ubuntu-18.04.1-desktop-amd64.manifest | sed -e 's#\t.*##g' )
Link for reference: https://askubuntu.com/questions/1087267/how-do-i-reinstall-the-software-packages-that-came-with-ubuntu-18-04