Copying and pasting data from Excel to Mathematica

Type into Mathematica ImportString["", "TSV"]

Paste the excel data between the empty double brackets.

Source: http://mathematica.stackexchange.com/questions/8997/cut-and-paste-data-from-a-spreadsheet

Mathematica: Clear all variables except one

To clear all variables except x, for example, then input the following

AppendTo[$ContextPath, "special`"];

special`x;

Source: http://mathematica.stackexchange.com/questions/10970/how-to-clear-all-variables-except-one

Add shortcut for quit kernel in Mathematica

1. Navigate to Program Files/Wolfram Research/.../.../SystemFiles/FrontEnd/TextResources/Windows/

2. Edit the KeyEventTranslations.tr file

3. Example: If you want to add a shortcut for quit kernel, then insert the following into the file:       

Item[KeyEvent["q", Modifiers -> {Control}],

               FrontEndExecute[

                       FrontEndToken[

                                SelectedNotebook[],

                                "EvaluatorQuit",

                                Automatic

                       ]

               ]

       ],

This will assign Ctrl+q as a shortcut for quit kernel

Mathematica: Derivatives involving absolute values

Use ComplexExpand. e.g. D[ComplexExpand@Abs[x-1],x]

Source: http://mathematica.stackexchange.com/questions/47100/derivative-of-the-absolute-value-function-in-mathematica-looks-very-different-fr