R: Create function that iteratively performs some analysis to pairs of rasters, based on their names

Question

I am having 2 sets of raster data and their names are:

ntl_'a number'.tif

pop_'a number'.tif

My goal is to create a function that reads the first pair of rasters (e.g., ntl_1.tif and pop_1.tif), then executes the below code and then repeats the process with the next pair:

library(raster)
library(DescTools)

#create a data.frame of values from the NTL and pop raster data
ntl = raster("path/ntl_1.tif")
vals_ntl <- as.data.frame(values(ntl))
ntl_coords = as.data.frame(xyFromCell(ntl, 1:ncell(ntl)))
combine <- as.data.frame(cbind(ntl_coords,vals_ntl))

pop<-raster("path/pop_1.tif")
pop = resample(pop, ntl, method = 'bilinear')
vals_pop <- as.data.frame(values(pop))

block.data <- as.data.frame(cbind(combine, vals_pop))

names(block.data)[3] <- "ntl"
names(block.data)[4] <- "pop"

block.data <- na.omit(block.data)

block.data = subset(block.data, select = -c(x, y))

# sort by ntl
block.data <-block.data[order(block.data$ntl),]

ntl_vector <- block.data[ , "ntl"]
pop_vector <- block.data[ , "pop"]

#compute gini index
Gini(ntl_vector, pop_vector, unbiased = FALSE)

My issue is with the code inside the function, I do not know how to properly make the syntax (the above code is for a pair of raster while I have hundreds of pairs). Hopefully I can get the results (i.e., the gini coefficient) of every pair in my console or, even better, in a data.frame. The data are here.

Answer 1

library(purrr)
library(fs)

raster_gini <- function(
    .ntl = "ntl_1.tif", 
    .pop = "pop_1.tif",
    .rdgal = TRUE
) {
  
  if(.rdgal) {
    
    ntl = raster(.ntl)
    vals_ntl <- as.data.frame(values(ntl))
    ntl_coords = as.data.frame(xyFromCell(ntl, 1:ncell(ntl)))
    combine <- as.data.frame(cbind(ntl_coords,vals_ntl))
    
    pop<-raster(.pop)
    pop = resample(pop, ntl, method = 'bilinear')
    vals_pop <- as.data.frame(values(pop))
    
    block.data <- as.data.frame(cbind(combine, vals_pop))
    
    #rename the columns
    names(block.data)[3] <- "ntl"
    names(block.data)[4] <- "pop"
    
    #remove NA values
    block.data <- na.omit(block.data)
    
    #remove the columns x & y
    block.data = subset(block.data, select = -c(x, y))
    
    # sort by ntl
    block.data <-block.data[order(block.data$ntl),]
    
    ntl_vector <- block.data[ , "ntl"]
    pop_vector <- block.data[ , "pop"]
    
    #compute gini index
    gini <- Gini(ntl_vector, pop_vector, unbiased = FALSE)
    
    c(ntl = .ntl, pop = .pop, gini = gini)
    
  } else {
    c(ntl = .ntl, pop = .pop)
  }
  
}


doc_paths_ntl <- fs::dir_ls("path_to_ntl_raster", glob = "*tif*") 

doc_paths_pop <- fs::dir_ls("path_to_pop_raster", glob = "*tif*") 


result_df <- purrr::map2_dfr(.x = doc_paths_ntl, .y = doc_paths_pop, .f = raster_gini)


result_df <- result_df |> 
  dplyr::mutate(ntl = basename(ntl)) |> 
  dplyr::mutate(pop = basename(pop))

result_df