Examining the data set

In the previous exercises you have seen how your data set got printed in the console (if not, just type present in the console and press enter). What you should see are four columns of numbers, each row representing a different year: the first entry in each row is simply the row number, the second is the year, and the third and fourth are the numbers of boys and girls born that year, respectively.

Note that the row numbers in the first column are not part of the present data set. R adds them as part of its printout to help you make visual comparisons. You can think of them as the index that you see on the left side of a spreadsheet. In fact, the comparison to a spreadsheet will generally be helpful. R has stored the data in a kind of spreadsheet or table called a data frame.

Let's have a look at how you can investigate the structure of the present data frame. A first way to do this is with dim(my_data_frame). This R function will give you the dimensions of your data frame. The first element is the number of rows, the second the number of columns.

You can also see the names of these columns (or variables) by using the names() function: names(my_data_frame).