create new variable from date data
===

Now my data frame is like below

> head(t.zoo)
   
                        cl      es
>2012-06-06 10:30:00.4  85.92 1300.00

>2012-06-06 10:30:00.9  85.85 1300.00

>2012-06-06 10:30:01.4  85.83 1299.75

>2012-06-06 10:30:01.9  85.83 1299.75

>2012-06-06 10:30:02.4  85.85 1299.75

>2012-06-06 10:30:02.9  85.87 1300.00


I have two questions, first is I would like to add a variable name for the first column and 2nd is i want to create a categorical variable to help me indicate 2010-06-06 (since there are 3 separate days)

What I should do for the date data?

Thanks


