Conditional statement in R based on multiple rasters

Question

I have:

• raster_1: an integer raster with non-sequential values i (101, 130, 240, 323)
• i: a watershed discharging X of sediment in the environment
• raster_2: represents the water quality for each watershed i with values ranging from 0 to 100,000 - named plume_i

I have ~400 rasters representing the water quality of 400 watersheds.

I would like to build a loop to set the values in raster_1 to NA for each zone (defined by the values: 101, 130, 240, 323 in raster_1) when raster_2 for the corresponding value (e.g., plume_101) is 0, using R.

For instance,

• When raster_1 = 101 & plume_101 = 0, assign NA to raster_1 otherwise return raster_1 values
• When raster_1 = 130 & plume 130 = 0, assign NA to raster_1 otherwise return raster_1 values
• When raster_1 = 240 & plume 240 = 0, assign NA to raster_1 otherwise return raster_1 values and so forth...

How can I do this?

Answer 1

If I understood, you will be overwriting raster_1, putting NA when the condition is met. Here, the key is get which fetches an object from the environment by a string name.

library(raster)

# we create some rasters with same extent
m = matrix(sample(c(101,130,240,323),100, replace = T), ncol = 10)
r = raster(m)
p_101 = matrix(sample(0:10, 100, replace = T), ncol = 10)
plume_101 = raster(p_101)
p_130 = matrix(sample(0:10, 100, replace = T), ncol = 10)
plume_130 = raster(p_130)
p_240 = matrix(sample(0:10, 100, replace = T), ncol = 10)
plume_240 = raster(p_240)
p_323 = matrix(sample(0:10, 100, replace = T), ncol = 10)
plume_323 = raster(p_323)


par(mfrow = c(2,2))
for(i in c(101,130,240,323)) {
  r[r[] == i & get(sprintf("plume_%s", i))[] == 0] = NA
  plot(r, main = i, col = c("gold", "blue","brown", "tomato", "green"))
}

In the plot you may see how subsequently NA are added in each iteration