adding different curves to plots in R - r

Question

I know I can add the same curve to each plot pane as a layer using lattice and latticeExtra R packages (see blow).
But suppose we wanted to add different curves to each plot pane.
For example, in the below example, I wonder how to add v1 only to the top plot, v2 to the bottom-left plot, and v3 to the bottom-right plot?
library(lattice)
library(latticeExtra)
set.seed(24)
v1 <- density(rnorm(1e3, 3.5))
v2 <- density(rnorm(1e3, 3))
v3 <- density(rnorm(1e3, 2.75))
foo <- xyplot((1:32*.01)~wt|gear , data = mtcars)
foo + layer(panel.polygon(v1, col = 2, alpha = 0.3))

Answer 1

Here is one option
foo +
layer(if(panel.number() == 3) {
panel.polygon(v1, col = 2, alpha = 0.3)
} else if(panel.number() == 1) {
panel.polygon(v2, col = 2, alpha = 0.3)
} else{
panel.polygon(v3, col = 2, alpha = 0.3)
})
data
library(lattice)
library(latticeExtra)
set.seed(24)
v1 <- density(rnorm(1e3, 3.5))
v2 <- density(rnorm(1e3, 3))
v3 <- density(rnorm(1e3, 2.75))
foo <- xyplot((1:32*.01)~wt|gear , data = mtcars)

Answer 2

You can do it with ggplot2 and facet_grid:
library(ggplot2)
library(dplyr)
# user data
v1 <- (rnorm(1e3, 3.5))
v2 <- (rnorm(1e3, 3))
v3 <- (rnorm(1e3, 2.75))
# Make df1 from user data and associate with add gear value in `mtcars`
df1 <- data.frame(wt = c(v1, v2, v3),
gear = as.factor(c(rep(3, 1000),
rep(4, 1000),
rep(5, 1000))))
# select data from mtcars and add user defined values (`val`)
df2 <- mtcars %>%
mutate(val = 1:32 * 0.01) %>%
remove_rownames() %>%
mutate(gear = as.factor(gear)) %>%
select(c(val, gear, wt))
ggplot(df2, aes(x = wt, y = val, #set up mapping with df2
fill = gear)) +
geom_density(data = df1, #make density plots of df1
aes(x = wt,
fill = gear),
inherit.aes = FALSE) + #next add points from df1
geom_point(data = df2, aes(x = wt, y = val), inherit.aes = FALSE) +
facet_grid(cols = vars(gear))
You can make the fill color more transparent by adding an alpha value to geom_density.