[R] rollapply and difftime

[Nordlund, Dan (DSHS/RDA)]

Another option

Daily$tmdiff <- with(Daily, c(NA, diff(Date, units='days')))


Hope this is helpful,

Dan

Daniel Nordlund, PhD
Research and Data Analysis Division
Services & Enterprise Support Administration
Washington State Department of Social and Health Services


> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Morway,
> Eric
> Sent: Thursday, May 26, 2016 5:00 PM
> To: R mailing list
> Subject: [R] rollapply and difftime
> 
> Technically, the code below works and results in a column that I'm interested
> in working with for further processing.  However, it is both inefficient on
> lengthy (>100 yr) daily time series and is, frankly, not the R way of doing
> things.  Using the 'Daily' data.frame provided below, I'm interested to know
> the propeR way of accomplishing this same task in an efficient manner.  I
> tried combinations of rollapply and difftime, but was unsuccessful.  Eric
> 
> Daily <- read.table(textConnection("     Date        Q
> 1911-04-01 4.530695
> 1911-04-02 4.700596
> 1911-04-03 4.898814
> 1911-04-04 5.097032
> 1911-04-05 5.295250
> 1911-04-06 6.569508
> 1911-04-07 5.861587
> 1911-04-08 5.153666
> 1911-04-09 4.445745
> 1911-04-10 3.737824
> 1911-04-11 3.001586
> 1911-04-12 3.001586
> 1911-04-13 2.350298
> 1911-04-14 2.661784
> 1911-04-16 3.001586
> 1911-04-17 2.661784
> 1911-04-19 2.661784
> 1911-04-28 3.369705
> 1911-04-29 3.001586
> 1911-05-20 2.661784"),header=TRUE)
> 
> Daily$Date <- as.Date(Daily$Date)
> Daily$tmdiff <- NA
> for(i in seq(2,length(Daily$Date),by=1)){
>   Daily$tmdiff[i] <- as.numeric(difftime(Daily$Date[i],Daily$Date[i-1]))
> }
> 
> 	[[alternative HTML version deleted]]
> 
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