I would just add, see
?strptime
for information about those date format specifications ( "%V" for example),
and an introduction to R's handling of date and date-time values.
And a few quick examples, to see that %V works as advertised:
> format( Sys.Date() , '%V')
[1] "19"
> format( as.Date('2018-1-1') , '%V')
[1] "01"
> format( as.Date('2018-1-8') , '%V')
[1] "02"
-Don
--
Don MacQueen
Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062
Lab cell 925-724-7509
On 5/9/18, 1:49 AM, "R-help on behalf of Jim Lemon"
<r-help-boun...@r-project.org on behalf of drjimle...@gmail.com> wrote:
Hi Shakeel,
Assuming that you are starting with a bunch of dates:
# make a vector of character strings that can be converted to dates
rep_dates<-paste(sample(1:30,500,TRUE),sample(1:12,500,TRUE),
sample(2013:2017,500,TRUE),sep="/")
# if this isn't your format, change it
date_format<-"%d/%m/%Y"
# create a data frame with a column of dates
rep_df<-data.frame(rep_dates=as.Date(rep_dates,format=date_format))
# add the week of the year
rep_df$rep_week<-format(rep_df$rep_dates,"%V")
# add the year
rep_df$rep_year<-format(rep_df$rep_dates,"%Y")
# get a table of the weekly counts by year
rep_tab<-table(rep_df$rep_week,rep_df$rep_year)
# get the row means (5 year averages)
rep5<-apply(rep_tab,1,mean)
# plot the 5 year weekly averages
plot(rep5,type="b",ylim=c(0,4),xlab="Week",ylab="Reports per week")
# add the 2017 weekly counts
points(rep_tab[,5],type="b",col="red")
legend(1,4,c("5 yr average","2017"),pch=1,lty=1,col=c("black","red"))
Jim
On Wed, May 9, 2018 at 4:37 PM, Shakeel Suleman
<shakeel.sule...@phe.gov.uk> wrote:
> Hi,
>
> I am fairly new to 'R' and would like advice on the following. I want to
calculate a weekly average number of reports (e.g. of flu, norovirus) based on
the same weeks for the last five years. I will then use this to plot a chart
with 52 points for the average based on the last five years; another line will
then plot the current year, enabling a comparison of current weekly counts
against a five year average for the same week. I would like some advice on how
this can be done in 'R' . My data is disaggregated data - with dates in the
format in 01/01/2018.
>
> Thanks
>
> Shakeel Suleman
>
>
>
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______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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