R help - Mar 2011 - Associating the day of week to a daily xts object

I have the following xts objetct "temp" 
 
> str(temp)
An ?xts? object from 2010-12-26 to 2011-03-05 containing:
  Data: num [1:70, 1] 2.95 0.852 -0.139 1.347 2.485 ...
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr "t_n"
  Indexed by objects of class: [POSIXct,POSIXt] TZ: GMT
  xts Attributes:  
 NULL

> temp
                  t_n
2010-12-26  2.9500000
2010-12-27  0.8520833
2010-12-28 -0.1390625
...........

I would like to associate another column with the day of week in the form of
1=Mon, 2=Tue, ..., 7=Sun
in order to obtain:
>newtemp
                  t_n                     dow
2010-12-26  2.9500000    7
2010-12-27  0.8520833    1
2010-12-28 -0.1390625    2
..............

How could make this in the shortest (and elegant?) way?

Ciao from Rome
Vittorio

Victor,

The "weekdays" function will return the days of the week (as a
character
vector of names) that a given vector of dates (Date or POSIXct) fall on.
These can then be converted into numbers using a look-up table/vector.  See
below for an example using the sample_matrix data included with the xts
package.

##

require(xts)
data(sample_matrix)
dates <- as.POSIXct(rownames(sample_matrix), format = "%Y-%m-%d")
dayLookup <- 1:7
names(dayLookup) <- c("Mon", "Tue", "Wed",
"Thu", "Fri", "Sat", "Sun")

datesDays <- dayLookup[weekdays(dates, abbreviate = TRUE)]
print(datesDays)

##
>From here, you can just add the "datesDays" vector as an
additional column
to the original data, e.g.
 xts(cbind(sample_matrix, dow =datesDays), order.by = dates).

HTH,

Francisco

On Mon, Mar 7, 2011 at 9:05 AM, Victor <vdemart@gmail.com> wrote:
> I have the following xts objetct "temp"
>
> > str(temp)
> An ‘xts’ object from 2010-12-26 to 2011-03-05 containing:
>  Data: num [1:70, 1] 2.95 0.852 -0.139 1.347 2.485 ...
>  - attr(*, "dimnames")=List of 2
>  ..$ : NULL
>  ..$ : chr "t_n"
>  Indexed by objects of class: [POSIXct,POSIXt] TZ: GMT
>  xts Attributes:
>  NULL
>
>
> > temp
>                  t_n
> 2010-12-26  2.9500000
> 2010-12-27  0.8520833
> 2010-12-28 -0.1390625
> ...........
>
> I would like to associate another column with the day of week in the form
> of 1=Mon, 2=Tue, ..., 7=Sun
> in order to obtain:
>
> >newtemp
>
>                  t_n                     dow
> 2010-12-26  2.9500000    7
> 2010-12-27  0.8520833    1
> 2010-12-28 -0.1390625    2
> ..............
>
> How could make this in the shortest (and elegant?) way?
>
> Ciao from Rome
> Vittorio
>
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