R help - May 2011 - days between dates

Hello, I have some unbalanced panel data that is measured on weekdays only
(i.e., excluding Saturday and Sunday).  I would like to get the number of
days between dates such that the number of days between a Friday and a
Monday is 1 (and not 3).  Here is some code to illustrate my problem:

library('Hmisc');

DATE <-
as.Date(c('2011-05-18','2011-05-19','2011-05-20','2011-05-23','2011-05-24','2011-05-25'),
'%Y-%m-%d');
TEMP <- c(100,105,110,95,90,95);
DAYS <- weekdays(DATE);

DF <- data.frame(DATE, TEMP, DAYS);
DF;

DF$DAYS.BETWEEN <- DF$DATE - Lag(DF$DATE);
DF;

Essentially, I want to get it so the variable DAYS.BETWEEN is equal to 1 for
observation number 4.  Any ideas?  Thank you.  Geoff

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Geoff,

I think you could write an if loop to solve this.

You could write:

for(i in 1:num_obs){

if(DAYS[i]=='Monday'){
DF$DAYS.BETWEEN[i]<-1
}
}

Where 'num_obs' is the total number of temperature observations you
have.
This would only be correct if you had no missing data on Fridays.  Also, if
you had any missing Mondays, the Tuesday 'DAYS.BETWEEN' would be a 5
instead
of a 2.

Maybe there's a better way to do this, but I think this should work as long
as you have a pretty complete record.

Billy

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Your request seems bizarre to me. If you really want to ignore the actual time
intervals, just do your analysis without the actual dates.

If you just want forward-looking time intervals, then put them in the correct
index locations.

?diff

c(diff(DF$DATE),1)
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Geoffrey Smith <gps@asu.edu> wrote:

Hello, I have some unbalanced panel data that is measured on weekdays only
(i.e., excluding Saturday and Sunday). I would like to get the number of days
between dates such that the number of days between a Friday and a Monday is 1
(and not 3). Here is some code to illustrate my problem:
library('Hmisc'); DATE <-
as.Date(c('2011-05-18','2011-05-19','2011-05-20','2011-05-23','2011-05-24','2011-05-25'),
'%Y-%m-%d'); TEMP <- c(100,105,110,95,90,95); DAYS <-
weekdays(DATE); DF <- data.frame(DATE, TEMP, DAYS); DF; DF$DAYS.BETWEEN <-
DF$DATE - Lag(DF$DATE); DF; Essentially, I want to get it so the variable
DAYS.BETWEEN is equal to 1 for observation number 4. Any ideas? Thank you. Geoff
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