[R] Creating dataframe of all possible variable combinations

[Hosack, Michael]

Hello,

I need to create a dataframe containing all possible combinations of 
three variables: SITE (101,102,103,104), WDAY (MON,TUE,WED,THR,FRI),
and TOD (MORN, AFTN). There should be a total of 40 unique combinations
in my dataframe. I used expand.grid() successfully(?) to create my 
dataframe, but then when I went to order it by SITE, the resultant 
dataframe only contained four rows, one for each site. There must 
be something about this function that I don't understand. Any advice
would be appreciated. 

Thank you,

Mike