Transform raster data to data.frame

Question

I have multiple rasters and the idea is to create a column for each layer inside a data frame, but I'd like to use mydf$layername or mydf[[layername]] operations in a loop. In my example:

library(raster)

Create an empty data frame:

mydf<-NULL

3 layers simulation:

## Create a simulated RBG rasters
r <- raster(nc=30, nr=30)
r <- setValues(r, round(runif(ncell(r))* 255))
g <- raster(nc=30, nr=30)
g <- setValues(r, round(runif(ncell(r))* 255))
b <- raster(nc=30, nr=30)
b <- setValues(r, round(runif(ncell(r))* 255))
rgb<-stack(r,g,b)

Population of data frame(mydf) with each layer information and use "names" as a variable name

for (i in 1:length(rgb@layers)){
mydf$assign(paste0(rgb[[i]]@layers)) <- as(as.im(rgb[[i]]), "SpatialGridDataFrame")$v
}
Error in mydf$assign(paste0(rgb[[i]]@data@names)) <- as(as.im(rgb[[i]]),  :

or


for (i in 1:length(rgb@layers)){
     mydf[[assign(paste0(rgb[[i]]@layers))]] <- as(as.im(rgb[[i]]), "SpatialGridDataFrame")$v
}
Error in paste0(rgb[[i]]@layers) :

There is any solution for this mydf$assign(paste0(rgb[[i]]@layers)) or mydf[[assign(paste0(rgb[[i]]@layers))]] operations?

Why are you using `assign()` here? Just use `mydf[[rgb[[i]]@data@names]]` (the `paste0()` isn't doing anything). — MrFlick, Nov 12 '20 at 21:52

Robert Hijmans · Accepted Answer · 2020-11-13T03:33:32.077

You are going about this very much the wrong way. You should not use @. For example, instead of rgb@layers use nlayers(rgb). Also, you should never use assign.

Example data

library(raster)
rgb <- brick(nc=10, nr=10, nl=3)
set.seed(1)
rgb <- setValues(rgb, round(runif(3 * ncell(r)) * 255))
names(rgb) <- c("R", "G", "B")

You do not need that loop at all. You can just do

v <- as.data.frame(rgb)
head(v)
    R   G   B
1  68 167  68
2  95  90  56
3 146  69 132
4 232 253  69
5  51 162  46
6 229  54 132

Or

v <- data.frame(values(rgb))

You could that with a loop. The easiest way would be to use a list

x <- list()
for (i in 1:nlayers(rgb)){
     x[[i]] <- values(rgb[[i]])
}

df <- data.frame(x)
colnames(df) <- names(rgb)

Transform raster data to data.frame

1 Answers1