[R] Runs of at least 5 days with certain value in a rasterbrick in R

[PIKAL Petr]

Hallo

I do not know anything about rasterbrick but what about splitting it to list according to season. If you have dates starting 1.12. and ending 28.2 as one season, diff should be 1day for each season. If you manage to correctly split your data, you can cycle through list or use lapply to get desired result.

Cheers
Petr

> -----Original Message-----
> From: R-help <r-help-bounces using r-project.org> On Behalf Of Adam Dragula
> Sent: Wednesday, January 20, 2021 10:46 PM
> To: R-help using r-project.org
> Subject: [R] Runs of at least 5 days with certain value in a rasterbrick in R
> 
> Dear R users,
> 
> I am  working with a rasterbrick named X, which has got 6300 time layers.
> Those 6300 time layers represent every winter day since 1.1.1950 till 31.12. I
> dropped all 29th of february so that I had 90 time layers for every season.
> Values throughout the whole domain are between 0.5 and 1.5. I successfully
> made a function, which creates a rasterlayer, which contains amount of runs
> of at least 5 days with values greater than 1.0. So for every grid point, I have
> got amount of events I am looking for. The function is following:
> 
> ff<-function(x,na.rm=TRUE){
> y<-x > 1
> n<- ave(y,cumsum(y == 0), FUN = cumsum)
> sum(n >= 5)
> }
> 
> This works very well, however, there is a problem. After layer which
> represents 28.2., 1.12., 2.12. and so on.. follows. It means, that event starting
> 28.2. may be detected if the criterion is satisfied throughout the first four
> days of following december. Of course I dont wanna detect such events as
> those are two distinct seasons. So I tried something like this (to somehow
> divide it into 70 seasons and calculate function ff for them):
> 
> indices<-rep(1:70,each=90)
> XX<-stackApply(X,indices,fun=ff)
> 
> At first sight, this works and no error is written. However, results are
> miscounted and there is too much events detected, for example 20 events
> are detected in the first layer at maximum, which doesnt make any sense
> (20x5=100, there is just 90 days per season). Other fact is, that this works
> perfectly fine, if I dont divide the whole series and use the criterion through
> original brick X without any indices.
> I cant see where the problem is, so every help is deeply appreciated, maybe
> another way could be more efficient.
> 
> Adam Dragula
> 
> 
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