This function correlates time series data to produce correlation and significance grids based on the chosen method.

gridcorts

#############################################################################################
# title         : Gridded Correlation of Time Series Raster Data (Gridcorts)
# purpose       : Pixelwise time series correlation and significance based on Pearson's r, 
#               : Spearman's rho or Kendall's tau
# author        : Abdulhakim Abdi (@HakimAbdi)
# input         : Raster brick comprising two time series of equal number of layers
# output        : Raster object of pixelwise correlation, significance or both (i.e. brick) 
#               : based on the chosen method
# update        : Minor based suggestion from Tao Xiong of Northeast Normal University in China.
# data          : Test data: https://1drv.ms/u/s!AsHsKb_qtbkwgvoQuHnPaFazPr_XnA?e=fJ9fue
#############################################################################################
# Please cite this paper if you use this code in a publication
#############################################################################################
# CITATION: Abdi, Abdulhakim M., et al. "The El Niño–La Niña cycle and recent trends in supply 
# and demand of net primary productivity in African drylands." Climatic Change 138.1-2 (2016): 111-125. 
# https://link.springer.com/article/10.1007/s10584-016-1730-1
#############################################################################################

gridcorts <- function(rasterstack, method, type=c("corel","pval","both")){
  # Values for (layers, ncell, ncol, nrow, method, crs, extent) come straight from the input raster stack
  # e.g. nlayers(rasterstack), ncell(rasterstack)... etc.
  print(paste("Start Gridcorts:",Sys.time()))
  print("Loading parameters")
  layers=nlayers(rasterstack);ncell=ncell(rasterstack);
  ncol=ncol(rasterstack);nrow=nrow(rasterstack);crs=crs(rasterstack);
  extent=extent(rasterstack);pb = txtProgressBar(min = 0, max = ncell, initial = 0)
  print("Done loading parameters")
  mtrx <- as.matrix(rasterstack,ncol=layers)
  empt <- matrix(nrow=ncell, ncol=2)
  print("Initiating loop operation")
  if (type == "corel"){
    for (i in 1:ncell){
      setTxtProgressBar(pb,i)
      if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){ 
        empt[i,1] <- NA 
      } else 
        if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
          empt[i,1] <- NA 
        } else 
          empt[i,1] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$estimate)
    }
    print("Creating empty raster")
    corel <- raster(nrows=nrow,ncols=ncol,crs=crs)
    extent(corel) <- extent
    print("Populating correlation raster")
    values(corel) <- empt[,1]
    print(paste("Ending Gridcorts on",Sys.time()))
    corel
  } 
  else
    if (type == "pval"){
      for (i in 1:ncell){
        setTxtProgressBar(pb,i)
        if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){ 
          empt[i,2] <- NA 
        } else 
          if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
            empt[i,2] <- NA 
          } else 
            empt[i,2] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$p.value)
      }
      pval <- raster(nrows=nrow,ncols=ncol,crs=crs)
      extent(pval) <- extent
      print("Populating significance raster")
      values(pval) <- empt[,2]
      print(paste("Ending Gridcorts on",Sys.time()))
      pval
    }
  else
    if (type == "both"){
      for (i in 1:ncell){
        setTxtProgressBar(pb,i)
        if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){ 
          empt[i,] <- NA 
        } else 
          if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
            empt[i,] <- NA 
          } else {
            empt[i,1] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$estimate) 
            empt[i,2] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$p.value)
          }
      }
      c <- raster(nrows=nrow,ncols=ncol,crs=crs)
      p <- raster(nrows=nrow,ncols=ncol,crs=crs)
      print("Populating raster brick")
      values(c) <- empt[,1]
      values(p) <- empt[,2]
      brk <- brick(c,p)
      extent(brk) <- extent
      names(brk) <- c("Correlation","Pvalue")
      print(paste("Ending Gridcorts on",Sys.time()))
      brk
    }
}

Hi! Thank you so much for uploading this code :) When ran I get the error: Error in match.arg(method) : object 'method' not found after inputting: gridcorts(s, method, type=c("both"))

try this: x <- gridcorts(s, method="pearson", type="both").

And thanks to the Author, i have been searching for something like this for a while!

try this: x <- gridcorts(s, method="pearson", type="both").

And thanks to the Author, i have been searching for something like this for a while!

Yep, that was the correct fix. Thanks!!

Hi, I'm glad this was resolved. Please also note that you can user either use "Pearson", "Spearman" or "Kendall" depending on what type of correlation you're interested in.

Hi,

Thanks a lot for your code I want to do exactly that for temperature and NDWI. I just have a question concerning the two plots that you put on your blog.

Do you have the code for this? I am blocked with cg1 and now I don't know what to do ?

Thanks again : )

Hi. I don't quite understand what you mean by "blocked with cg1". These plots were produced using the code and data that are on the blog post: https://hakimabdi.com/blog/test-pixelwise-correlation-between-two-time-series-of-gridded-satellite-data-in-r

…

On Fri, 5 Mar 2021 at 21:31, poussinc ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ Hi, Thanks a lot for your code I want to do exactly that for temperature and NDWI. I just have a question concerning the two plots that you put on your blog. [image: image] <https://user-images.githubusercontent.com/47449630/110170062-e8250100-7df9-11eb-9685-8d82c91eb024.png> Do you have the code for this? I am blocked with cg1 and now I don't know what to do ? Thanks again : ) — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/7308bbd6d9d94cf0a1b8#gistcomment-3655230>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AASV4HZ4PTTTYRH63L47UH3TCE5RFANCNFSM4XVVHTRA> .

Thanks Hakim for your answer. Maybe I do something wrong in the script because i Have this result:

and so I cannot see the images. Maybe you have an idea because I have this result ?

Thanks a lot Charlotte

This could happen in one of two cases, either (1) the layers mostly have NA values or (2) they have less than 4 data values in which case a correlation cannot be established. Can you please tell me what data you're trying to correlate?

…

On Mon, 15 Mar 2021 at 14:39, poussinc ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ Thanks Hakim for your answer. Maybe I do something wrong in the script because i Have this result: [image: image] <https://user-images.githubusercontent.com/47449630/111162055-0cbc6e00-859c-11eb-8ba0-eeb8b7878130.png> and so I cannot see the images. Maybe you have an idea because I have this result ? Thanks a lot Charlotte — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/7308bbd6d9d94cf0a1b8#gistcomment-3665567>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AASV4H7P34JO4EPLPCXVFALTDYEZFANCNFSM4XVVHTRA> .

Hello Hakim,
I have been looking for a solution like this. However, I am getting an error:

[1] "Start Gridcorts: 2021-06-27 20:51:27"
[1] "Loading parameters"
[1] "Done loading parameters"
[1] "Initiating loop operation"
==========Error in match.arg(alternative) : 'arg' must be of length 1
In addition: There were 50 or more warnings (use warnings() to see the first 50)

warnings()
Warning messages:
1: In cor(x, y) : the standard deviation is zero
2: In cor(x, y) : the standard deviation is zero
3: In cor(x, y) : the standard deviation is zero
4: In cor(x, y) : the standard deviation is zero
5: In cor(x, y) : the standard deviation is zero
6: In cor(x, y) : the standard deviation is zero
7: In cor(x, y) : the standard deviation is zero
8: In cor(x, y) : the standard deviation is zero
9: In cor(x, y) : the standard deviation is zero
10: In cor(x, y) : the standard deviation is zero
11: In cor(x, y) : the standard deviation is zero
12: In cor(x, y) : the standard deviation is zero
13: In cor(x, y) : the standard deviation is zero
14: In cor(x, y) : the standard deviation is zero
15: In cor(x, y) : the standard deviation is zero
16: In cor(x, y) : the standard deviation is zero
17: In cor(x, y) : the standard deviation is zero
18: In cor(x, y) : the standard deviation is zero
19: In cor(x, y) : the standard deviation is zero
20: In cor(x, y) : the standard deviation is zero

Can you point me in the right direction to resolve this?

HI. I'm not sure why the warning is happening, to be frank, but I have a suspicion that it has something to do with the distribution of your data. Please make sure that the layers you're trying to do not all have the same values or are not all NA. As far as the error is concerned, please post the full code that led up to it because it could be the type of data you're using. Note that your layers have to match in order for a correlation to be made on a pixelwise basis.

…

On Sun, 27 Jun 2021 at 21:10, Faustin Gashakamba ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ Hello Hakim, I have been looking for a solution like this. However, I am getting an error: [1] "Start Gridcorts: 2021-06-27 20:51:27" [1] "Loading parameters" [1] "Done loading parameters" [1] "Initiating loop operation" ==========Error in match.arg(alternative) : 'arg' must be of length 1 In addition: There were 50 or more warnings (use warnings() to see the first 50) warnings() Warning messages: 1: In cor(x, y) : the standard deviation is zero 2: In cor(x, y) : the standard deviation is zero 3: In cor(x, y) : the standard deviation is zero 4: In cor(x, y) : the standard deviation is zero 5: In cor(x, y) : the standard deviation is zero 6: In cor(x, y) : the standard deviation is zero 7: In cor(x, y) : the standard deviation is zero 8: In cor(x, y) : the standard deviation is zero 9: In cor(x, y) : the standard deviation is zero 10: In cor(x, y) : the standard deviation is zero 11: In cor(x, y) : the standard deviation is zero 12: In cor(x, y) : the standard deviation is zero 13: In cor(x, y) : the standard deviation is zero 14: In cor(x, y) : the standard deviation is zero 15: In cor(x, y) : the standard deviation is zero 16: In cor(x, y) : the standard deviation is zero 17: In cor(x, y) : the standard deviation is zero 18: In cor(x, y) : the standard deviation is zero 19: In cor(x, y) : the standard deviation is zero 20: In cor(x, y) : the standard deviation is zero Can you point me in the right direction to resolve this? — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <https://gist.github.com/7308bbd6d9d94cf0a1b8#gistcomment-3794782>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AASV4H5ZH5IPL5FA3XVQ7PLTU5ZRXANCNFSM4XVVHTRA> .

Hi Hakim,

thank you very much for your code, it is amazing!
Here we calculate the correlation at time lag 0. I want to observe the time lag response and the maximum correlation at time lag = 0, 1, 2, 3, 4. Do you have an idea how to do this with raster brick data ?

thank you in advance

Warning in install.packages :
package ‘gridcorts’ is not available (for R version 3.6.3)

#while executing the package on data
Error in gridcorts(rasterstack = rstack, method = "pearson", type = "both") :
could not find function "gridcorts"
Timing stopped at: 0 0 0

Could you help me to solve this issue?

library (raster) library(spatial)library(rgdal)library(rgeos)library(sp)library(maptools)library(Kendall)`

setwd ("E:/Central University of Jharkhand/M.Sc dissertation")

D <- ("E:/Central University of Jharkhand/M.Sc dissertation/DEMClipped.tif")
DEM <- raster ("DEMClipped.tif")
Temp <- ("E:/Central University of Jharkhand/M.Sc dissertation/MAAT_Clipped.tif")
MAAT <- raster ("MAAT_Clipped.tif")

s <- stack (DEM, MAAT)
a <- length (MAAT)
b <- length (DEM)

#Slope Function
fun = function(x) {if (is.na(x[1])) else {lm(x[1] ~ x[2])$coefficients[2]}}
slope <- calc(s, fun)

I am using this code to run a linear regression between the temperature raster layer and DEM. But in slope, I am NA and NA as max and min values and thereafter a blank map when I am plotting the same. Please help! I need to calculate Lapse rate raster from it.

Hi,

I am excited to use this code. When I try to run the code with the sample data I can't get it to not give me NAs. Am I reading in the files incorrectly?

require(raster)
npp<-raster("C:/Users/folder/Downloads/gridcorts_data/npp.tif")
rainfall<-raster("C:/Users/folder/Downloads/gridcorts_data/rain.tif")
rstack <- stack(npp,rainfall)
cg1 <- gridcorts(rasterstack = rstack, method = "spearman",type="both")

I figured out I need to use the "stack" function to read in all the bands of the raster. The gridcorts function works now.

For example:
npp<-stack("C:/Users/folder/Downloads/gridcorts_data/npp.tif")

Thank you very much. Please tell me how to get the correlation image?
require(raster)
npp<-raster("C:/Users/User/OneDrive/Desktop/Corr/npp.tif")
rainfall<-raster("C:/Users/User/OneDrive/Desktop/Corr/rain.tif")
rstack <- stack(npp,rainfall)
gridcorts <- function(rasterstack, method, type=c("corel","pval","both")){

Values for (layers, ncell, ncol, nrow, method, crs, extent) come straight from the input raster stack

e.g. nlayers(rasterstack), ncell(rasterstack)... etc.

print(paste("Start Gridcorts:",Sys.time()))
print("Loading parameters")
layers=nlayers(rasterstack);ncell=ncell(rasterstack);
ncol=ncol(rasterstack);nrow=nrow(rasterstack);crs=crs(rasterstack);
extent=extent(rasterstack);pb = txtProgressBar(min = 0, max = ncell, initial = 0)
print("Done loading parameters")
mtrx <- as.matrix(rasterstack,ncol=layers)
empt <- matrix(nrow=ncell, ncol=2)
print("Initiating loop operation")
if (type == "corel"){
for (i in 1:ncell){
setTxtProgressBar(pb,i)
if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){
empt[i,1] <- NA
} else
if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
empt[i,1] <- NA
} else
empt[i,1] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$estimate)
}
print("Creating empty raster")
corel <- raster(nrows=nrow,ncols=ncol,crs=crs)
extent(corel) <- extent
print("Populating correlation raster")
values(corel) <- empt[,1]
print(paste("Ending Gridcorts on",Sys.time()))
corel
}
else
if (type == "pval"){
for (i in 1:ncell){
setTxtProgressBar(pb,i)
if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){
empt[i,2] <- NA
} else
if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
empt[i,2] <- NA
} else
empt[i,2] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$p.value)
}
pval <- raster(nrows=nrow,ncols=ncol,crs=crs)
extent(pval) <- extent
print("Populating significance raster")
values(pval) <- empt[,2]
print(paste("Ending Gridcorts on",Sys.time()))
pval
}
else
if (type == "both"){
for (i in 1:ncell){
setTxtProgressBar(pb,i)
if (all(is.na(mtrx[i,1:(layers/2)])) | all(is.na(mtrx[i,((layers/2)+1):layers]))){
empt[i,] <- NA
} else
if (sum(!is.na(mtrx[i,1:(layers/2)]/mtrx[i,((layers/2)+1):layers])) < 4 ){
empt[i,] <- NA
} else {
empt[i,1] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$estimate)
empt[i,2] <- as.numeric(cor.test(mtrx[i,1:(layers/2)], mtrx[i,((layers/2)+1):layers],method=method)$p.value)
}
}
c <- raster(nrows=nrow,ncols=ncol,crs=crs)
p <- raster(nrows=nrow,ncols=ncol,crs=crs)
print("Populating raster brick")
values(c) <- empt[,1]
values(p) <- empt[,2]
brk <- brick(c,p)
extent(brk) <- extent
names(brk) <- c("Correlation","Pvalue")
print(paste("Ending Gridcorts on",Sys.time()))
brk
}
}

cg1 <- gridcorts(rasterstack = rstack, method = "spearman",type="both")