Getting coordinates of pixels which values are equal to 0 - r

Question

I have a raster map with 202 rows and 201 columns
there are some grids in this map which pixel values is 0
I want to write a function that return all the pixel values 0 grids' coordinate
how can I do it
I was trying to use if loop and while loop
but it always says TRUE/FALSE need
here is my sample code
library(raster)
library(rgdal)
library(maptools)
library(sp)
setwd("E:/Landsat-data-NASA atm-corrected/sample_day1")
restdir2 <- ("E:/Landsat-data-NASA atm-corrected/sample_day1")
n3 <- list.files(restdir2, pattern="*band4_clip_1.tif", full.names=TRUE)
n4 <- list.files(restdir2, pattern="*cloud_qa_clip_1.tif", full.names=TRUE)
n5 <- list.files(restdir2, pattern="*cloud.tif", full.names=TRUE)
create<- function(x,y)
{
layer <- raster(n4)
layer2 <- raster(n3)
for(c in 1:x)
{
for(r in 1:y)
{
nl<- layer2
if(layer[c,r]==0)
return layer[c,r]
}
}
}
create (10,10)

Answer 1

Here are two (very similar) approaches
library(raster)
# set up example data
r <- raster(nrow=18, ncol=36)
set.seed(0)
r[] <- round(runif(ncell(r)) * 10 - 5)
# approach 1, for a single layer
p <- rasterToPoints(r, fun=function(x){x == 0})
# approach 2, also works for multiple layers
# first remove all non zero cells
z <- subs(r, data.frame(0, 1))
p <- rasterToPoints(z)
# results
plot(r)
points(p[,1:2])
if you have multiple layers with the same spatial parameters (extent and resolution)
# create example data
x1 <- setValues(r, round(runif(ncell(r)) * 10 - 5))
x2 <- setValues(r, round(runif(ncell(r)) * 10 - 5))
x3 <- setValues(r, round(runif(ncell(r)) * 10 - 5))
# combine layers
s <- stack(x1, x2, x3)
z <- subs(r, data.frame(0, 1))
p <- rasterToPoints(z)