Plotting family of functions with qplot without duplicating data - r

Question

Given family of functions f(x;q) (x is argument and q is parameter) I'd like to visulaize this function family on x taking from the interval [0,1] for 9 values of q (from 0.1 to 0.9). So far my solution is:
f = function(p,q=0.9) {1-(1-(p*q)^3)^1024}
x = seq(0.0,0.99,by=0.01)
q = seq(0.1,0.9,by=0.1)
qplot(rep(x,9), f(rep(x,9),rep(q,each=100)), colour=factor(rep(q,each=100)),
geom="line", size=I(0.9), xlab="x", ylab=expression("y=f(x)"))
I get quick and easy visual with qplot:
My concern is that this method is rather memory hungry as I need to duplicate x for each parameter and duplicate each parameter value for whole x range. What would be alternative way to produce same graph without these duplications?

Answer 1

At some point ggplot will need to have the data available to plot it and the way that package works prohibits simply doing what you want. I suppose you could set up a blank plot if you know the x and y axis limits, and then loop over the 9 values of q, generating the data for that q, and adding a geom_line layer to the existing plot object. However, you'll have to produce the colours for each layer yourself.
If this is representative of the size of problem you have, I wouldn't worry too much about the memory footprint. We're only talking about a two vectors of length 900
> object.size(rnorm(900))
7240 bytes
and the 100 values over the range of x appears sufficient to give a smooth plot.
for loop to add layers to ggplot
require("ggplot2")
## something to replicate ggplot's colour palette, sure there is something
## to do this already in **ggplot** now...
ggHueColours <- function(n, h = c(0, 360) + 15, l = 65, c = 100,
direction = 1, h.start = 0) {
turn <- function(x, h.start, direction) {
(x + h.start) %% 360 * direction
}
if ((diff(h) %% 360) < 1) {
h[2] <- h[2] - 360 / n
}
hcl(h = turn(seq(h[1], h[2], length = n), h.start = h.start,
direction = direction), c = c, l = l)
}
f = function(p,q=0.9) {1-(1-(p*q)^3)^1024}
x = seq(0.0,0.99,by=0.01)
q = seq(0.1,0.9,by=0.1)
cols <- ggHueColours(n = length(q))
for(i in seq_along(q)) {
df <- data.frame(y = f(x, q[i]), x = x)
if(i == 1) {
plt <- ggplot(df, aes(x = x, y = y)) + geom_line(colour = cols[i])
} else {
plt <- plt + geom_line(data = df, colour = cols[i])
}
}
plt
which gives:
I'll leave the rest to you - I'm not familiar enough with ggplot to draw a legend manually.