Duplicate App Icons on iPhone

"I have duplicate app icons on my iPhone screen. I do not know what caused this, but I do not want duplicate app icons."

This quote is from an earlier question that is now closed. The solution was a factory reset

My answer: There are 2 icons for each app one at the Home Screen and one in the App Library. If you have 2 icons at the Home Screen then drag it to the one in the App Library. And it is gone. 

If you actually want an app icon in more than one copy you can make several by drag them from App Library.