title: How to add a column in the data frame within a function
body: <p>I have a data frame, and I want to do some calculation with existing columns and create new column in my data set which is a combination of existing... I can do this easily outside function... but if I wrap the code witin function, the changes I made (inside functions) are not visible outside function... i.e. the new column doesn't exist...</p>
  
  <p>I would appreciate sample code to do this...</p>