O statements (put and input functions)
put () function: the variables into numeric or character string variables (output variables)
input () function: the string variables into numeric variable (input variable)
Select and delete statements (keep, drop function)
keep function: select a variable, the value of the column
drop function: delete a variable, column values
From the entire operating speed of view, then, the first fastest and slowest third
drop function and keep functions are reversed, the same usage, for example not
Determine the filter statement (where, if the function)
where judgment statement: a data process step or steps statement for screening data
if conditional statement: Step for data, the filtered data is determined
Conditional statement (if-then-else function)
