title: how to tell R to count correctly the numer of subjects in long format file?
body: <p>I have a csv file that I loaded to R. It is built in long format with
  each subject underwent several observations. Therefore, in the column &quot;subject&quot;, subject number 1 appeared in 30 cells in this column, for example, and so the other 51 subjects. R is relating to the total number of subjects as 1530 instead of 51!!</p>
  <p>How can I tell R to count the number of subjects correctly?</p>