Plotting only raster cells that fall within boundaries of another raster in R

Question

I've got two rasters, soil and slope. I want to plot the slope raster but only in areas where there is soil (i.e. soil is > 0). How can I do this?

This is the soil raster:

This is the slope raster:

EDIT 1: more information about the rasters.

soil

 > extent(soil)
 class      : Extent 
 xmin       : -180 
 xmax       : 179.9856 
 ymin       : -60 
 ymax       : 89.994 
 > res(soil)
 [1] 0.008333 0.008333
 > origin(soil)
 [1]  0.001133 -0.002400  

slope

 > extent(slope)
class      : Extent 
xmin       : -180 
xmax       : 180.0023 
ymin       : -56.00016 
ymax       : 84.00257 
> res(slope)
[1] 0.008333386 0.008333496
> origin(slope)
[1] 0.0011330 0.0009332

EDIT 2: information about dimensions

 > dim(soil)
 [1] 18000 43200     1

 > dim(slope)
 [1] 16800 43200     1

Answer 1

require(raster)

# make 2 dummy rasters, different extents but same origin and resolution. Values 1:6
slope <- raster(xmn = 0, xmx = 5, ymn = 0, ymx = 5, res = 1)
slope[] <- sample(1:6, ncell(slope), replace = T)

soil <- raster(xmn = 0, xmx = 7, ymn = -1, ymx = 4, res = 1)
soil[] <- sample(1:6, ncell(soil), replace = T)

# create your blank raster to populate. This is only the area both inputs occupy.
r_intersec <- raster(raster::intersect(slope,soil))

# The other 2 rasters should be cropped to the extent of your target raster, to avoid extent errors as mentioned in the comments
croped_slope <- crop(slope,extent(r_intersec))
croped_soil <- crop(soil,extent(r_intersec))

tmp <- croped_slope
tmp[which(croped_soil[] <= 0)] <- NA

par(mfrow=c(1,3))
plot(slope)
plot(soil)
plot(tmp)

*raster sample and crop idea from https://gis.stackexchange.com/a/328883/77836