title: Finding the max of one column when values in another column is X
body: <p>how do you find the max value of one column (column B) when the values of Column C = X.  How would I keep the label from Column A.  Let's say my data is called my.data, column a = Country name, column b = number of children born and column C = year the child was born.  So how do find the maximum number of children born in year 2001, keeping the name of the country in line?</p>
  
  <p>Thanks, I'm very sorry, I'm new to R</p>