[R] need to delete by time, not date

[David Winsemius]

On May 10, 2011, at 11:06 AM, Schatzi wrote:

> I have a matrix where one column has a date and another column has a  
> time. I
> need to delete all times before 6am. I had combined the Date and  
> Time column
> into DateTime.
>
> Mat1:
> Weight     Date  Time
> 7.6 04/28/11 09:03
> 8.4 04/29/11 03:11
> 8.6 04/29/11 05:32
> 8.6 04/29/11 09:53
> 1.4 05/01/11 19:52
>
> I tried just picking up the time:
>
> as.POSIXct(Mat1$Time, format = "%H:%M")
>
> but this assigns the time value today's date.

Since these are either character strings (or factors) at the  
moment ... and if they are matrices they are character...

Mat1[Mat1$Time >= "06:00" , ]

If actually a dataframe then

Mat1[as.character(Mat1$Time) >= "06:00" , ]

In the future please include the output of dput(Mat1).

>
> The final matrix should look like:
> Weight     Date  Time
> 7.6 04/28/11 09:03
> 8.6 04/29/11 09:53
> 1.4 05/01/11 19:52
>
>

David Winsemius, MD
West Hartford, CT