[R] inefficient for loop, is there a better way?

[William Dunlap]

Try using stats::filter (not the unfortunately named dplyr::filter, which
is entirely different).
state>elev is a logical vector, but filter(), like most numerical
functions, treats TRUEs as 1s
and FALSEs as 0s.

E.g.,

> str( stats::filter( x=examp$stage>elev1, filter=rep(1,7),
method="convolution", sides=1) )
 Time-Series [1:1000] from 1 to 1000: NA NA NA NA NA NA 3 3 2 2 ...
> str( stats::filter( x=examp$stage>elev2, filter=rep(1,7),
method="convolution", sides=1) )
 Time-Series [1:1000] from 1 to 1000: NA NA NA NA NA NA 1 2 1 1 ...


Bill Dunlap
TIBCO Software
wdunlap tibco.com

On Tue, Dec 12, 2017 at 5:36 PM, Morway, Eric <emorway at usgs.gov> wrote:

> The code below is a small reproducible example of a much larger problem.
> While the script below works, it is really slow on the true dataset with
> many more rows and columns.  I'm hoping to get the same result to examp,
> but with significant time savings.
>
> The example below is setting up a data.frame for an ensuing regression
> analysis.  The purpose of the script below is to appends columns to 'examp'
> that contain values corresponding to the total number of days in the
> previous 7 ('per') above some stage ('elev1' or 'elev2').  Is there a
> faster method that leverages existing R functionality?  I feel like the
> hack below is pretty clunky and can be sped up on the true dataset.  I
> would like to run a more efficient script many times adjusting the value of
> 'per'.
>
> ts <- 1:1000
> examp <- data.frame(ts=ts, stage=sin(ts))
>
> hi1 <- list()
> hi2 <- list()
> per <- 7
> elev1 <- 0.6
> elev2 <- 0.85
> for(i in per:nrow(examp)){
>     examp_per <- examp[seq(i - (per - 1), i, by=1),]
>     stg_hi_cond1 <- subset(examp_per, examp_per$stage > elev1)
>     stg_hi_cond2 <- subset(examp_per, examp_per$stage > elev2)
>
>     hi1 <- c(hi1, nrow(stg_hi_cond1))
>     hi2 <- c(hi2, nrow(stg_hi_cond2))
> }
> examp$days_abv_0.6_in_last_7   <- c(rep(NA, times=per-1), unlist(hi1))
> examp$days_abv_0.85_in_last_7  <- c(rep(NA, times=per-1), unlist(hi2))
>
>         [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/
> posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

	[[alternative HTML version deleted]]