[R] subset POSIXct

[Keith Jones]

Hi,

I have a data frame with two columns: dt and tf.  The dt column is  
datetime and the tf column is a temperature.

                                dt  tf
1 2009-06-20 00:53:00 73
2 2009-06-20 01:08:00 73
3 2009-06-20 01:44:00 72
4 2009-06-20 01:53:00 71
5 2009-06-20 02:07:00 72
...

I need a subset of the rows where the minutes are 53.  The hour is  
immaterial.  I can not find a wildcard character to use to select the  
rows.

as.character(wtd$dt) %in% "2009-06-21 ??:53:00" or as.character(wtd 
$dt) %in% "2009-06-21 **:53:00" does not work.

What would you recommend?

Thanks,

Keith Jones, Ph.D.
VTS Pumps