title: How to assign variable from columns in an excel sheet in R studio
body: <p>I want to take averages of certain columns in my excel sheet that I have imported into R Studio but I am not sure how. For example,  I have the column "period type" and I want to take the average of the number of sales associated with "period type". But before I take the average of sales, how do I pull the column from my excel sheet if the excel sheet has already been imported?</p>