# [R] calculating a linear regression for each grid cell. firstly

ahmet varlı v@r||61 @end|ng |rom w|ndow@||ve@com
Wed Sep 9 16:13:51 CEST 2020

```       Hi all,

for example, � have 4 raster data and � try to convert these rasters to 1 array and calculate a linear regression for each grid cell how can � do this?

max_consecutive_days_1<- raster(ncol=94, nrow=192, xmn=-180, xmx=180, ymn=-90, ymx=90)
max_consecutive_days_2<- raster(ncol=94, nrow=192, xmn=-180, xmx=180, ymn=-90, ymx=90)
max_consecutive_days_3<- raster(ncol=94, nrow=192, xmn=-180, xmx=180, ymn=-90, ymx=90)
max_consecutive_days_4<- raster(ncol=94, nrow=192, xmn=-180, xmx=180, ymn=-90, ymx=90)

values(max_consecutive_days_1)  <- 1:ncell(max_consecutive_days_1)
values(max_consecutive_days_2) <- 1:ncell(max_consecutive_days_2)
values(max_consecutive_days_3) <- 1:ncell(max_consecutive_days_3)
values(max_consecutive_days_4) <- 1:ncell(max_consecutive_days_4)
set.seed(0)
values(max_consecutive_days_1)  <- runif(ncell(max_consecutive_days_1))
values(max_consecutive_days_2) <- runif(ncell(max_consecutive_days_2))
values(max_consecutive_days_3) <- runif(ncell(max_consecutive_days_3))
values(max_consecutive_days_4) <- runif(ncell(max_consecutive_days_4))

I tried to convert raster to an array and calculate a linear regression for each cell with these codes. there is something wrong in codes but I didn't find what it's wrong

library(raster)
r<-raster("C:/max_consecutive_days_1.tif")
a<-array(NA,dim=c(dim(r)[1:2],4))
i <- 1
dir.in <- "C:/max_consecutive_days/"
for (year in 1:4) {
fi<-paste0(dir.in,"max_consecutive_days_",year,".tif")
r<-raster(fi)
a[,,i]<-getValues(r,format="matrix")
i<-i+1
}

lmfunction <- function(x){

if (is.na(x[1])){ NA }

else

y<-c(1:length(x))
m1<- summary(lm(x~y))
coef <- m1\$coef[2]

coef
}

storem <- array(NA,dim=dim(a)[1:2])
for(i in 1:94){
for(j in 1:192){
tst<-mean(a[i,j,],n.rm=T)
if (is.na(tst)==F){
storem[i,j]<-lmfunction(a[i,j,])
}
}
}

Best wishes,