IDW parameters in R - r

Question

I want to perform IDW interpolation using R using the idw command from the gstat package. I have this data:
#settings
library(gstat)
library(dplyr)
library(sp)
library(tidyr)
id_rep <- rep(c(1,2), 20)
f <- rep(c(930,930.2), each=20)
perc <- rep(c(90, 80), each=10)
x <- sample(1:50, 40)
y <- sample(50:100, 40)
E <- runif(40)
df <- data.frame(id_rep, perc, x,y, f, E)
df_split <- split(df, list(df$id_rep, df$perc, df$f), drop = TRUE, sep="_")
#grid
x.range <- range(df$x)
y.range <- range(df$y)
grid <- expand.grid(x = seq(x.range[1], x.range[2], by=1),
y = seq(y.range[1], y.range[2], by=1))
coordinates(grid) <- ~x + y
#interpolation
lst_interp_idw <- lapply(df_split, function(X) {
coordinates(X) <- ~x + y
E_idw <- idw(E~ 1, X, grid, idp=1, nmax=3) %>% as.data.frame()
df_interp <- select(E_idw, x,y,E_pred=var1.pred)
df_interp
})
df_interp_idw <- bind_rows(lst_interp_idw, .id = "interact") %>%
separate(interact, c("id_rep", "perc", "f"), sep = "\\_")
Now I want to perform each run with different idp and nmax parameters within certain values​ (idp from 1 to 3 by 0.5, and nmax 3 to 6 by 1) and get out a data frame with columns for each combination of idp and nmax values. I try with two for loops but it doesn't work.
EDIT
the code that doesn't work is:
idp = seq(from = 1, to = 3, by = 0.5)
nmax = seq(from = 3, to = 6, by = 1)
...
for(i in idp) {
for(j in nmax)
{ E_idw= idw(E ~ 1, X, grid, nmax = i, idp = j)
}
}
...

Answer 1

Here is a way how to store the result of every iteration in a list.
#settings
#install.packages("gstat")
library(gstat)
library(dplyr)
library(sp)
library(tidyr)
id_rep <- rep(c(1,2), 20)
f <- rep(c(930,930.2), each=20)
perc <- rep(c(90, 80), each=10)
x <- sample(1:50, 40)
y <- sample(50:100, 40)
E <- runif(40)
df <- data.frame(id_rep, perc, x,y, f, E)
df_split <- split(df, list(df$id_rep, df$perc, df$f), drop = TRUE, sep="_")
#grid
x.range <- range(df$x)
y.range <- range(df$y)
grid <- expand.grid(x = seq(x.range[1], x.range[2], by=1),
y = seq(y.range[1], y.range[2], by=1))
coordinates(grid) <- ~x + y
# ==============================================
# NEW function
# ==============================================
idp = seq(from = 1, to = 3, by = 0.5)
nmax = seq(from = 3, to = 6, by = 1)
#interpolation
lst_interp_idw <- lapply(df_split, function(X) {
coordinates(X) <- ~x + y
df_interp <- vector(length(idp)*length(nmax), mode = "list" )
k <- 0
for(i in idp) {
for(j in nmax) {
print(paste(i, j))
# Iterator
k <- k + 1
E_idw= idw(E ~ 1, X, grid, nmax = i, idp = j) %>% as.data.frame()
df_interp[[k]] <- select(E_idw, x,y,E_pred=var1.pred)
}
}
return(df_interp)
})
# ==============================================
Some plausibility checks (lapply is applied to 8 list elements and 20 variations are calculated):
length(lst_interp_idw) # 8
length(lst_interp_idw[[1]]) #20
length(lst_interp_idw[[1]]) #20
It should be easy for you to adapt the last line of your code
df_interp_idw <- bind_rows(lst_interp_idw, .id = "interact") %>%
separate(interact, c("id_rep", "perc", "f"), sep = "\\_")
to format the output in the desired format. This highly depends on how you want to present the different interpolation alternatives.