I am very new to R. I am trying to create a function where the user is able to input expressions into arguments. These inputs are then used in plot3d through the rgl package. The function I have so far is :
flight_sim <- function(xval, yval, zval)
{
# Evaluate arguments and convert them into expressions
eval(parse(text = zval))
z <- data.frame(zval)
eval(parse(text = xval))
x <- data.frame(xval)
eval(parse(text = yval))
y <- data.frame(yval)
flight_path <- as.data.frame(cbind(x,y,z))
}
I have a readline() and switch() command :
cat('Select the flight path you wish to plot from the list below :
1. Helix
2. Conical
3. Spherical
4. Define your own flight path...')
userplot <- readline('Enter number here : ') # Allow user to enter choice from above
switch(userplot,"1"=flight_sim( sin(z), 1-cos(z), seq(0,20, pi/32) ),
"2"=flight_sim( z*cos(6*z), z*sin(6*z), seq(0,10, pi/64) ),
"3"=flight_sim( sin(z)*cos(20*z), sin(z)*sin(20*z), seq(0,pi,pi/399)),
"4"=custom())
Where custom() just prompts the user via readline() to enter x, y and z values, which is then followed by eval() and parse() and it works fine.
The problem I've been having is that x and y need to be functions of z, and this causes an error :
Error in parse(text = xval) : object 'z' not found
I thought by making the flight_sim function evaluate the zval argument first that it would fix it, however as I'm new to R I'm just getting more and more lost.
I hope what I have explained here makes some sense. I appreciate any help that can be provided.
Nothing is being passed as text in your example so using parse() doesn't seem necessary. If you want to delay evaulation, the best way would be to use substitute to grab the parameters as promises and then evaluate them in the context of your fliht_sim function. Here's what that would look like
flight_sim <- function(xval, yval, zval) {
z <- eval(substitute(zval))
x <- eval(substitute(xval))
y <- eval(substitute(yval))
data.frame(x,y,z)
}
userplot="2"
x <- switch(userplot,"1"=flight_sim( sin(z), 1-cos(z), seq(0,20, pi/32) ),
"2"=flight_sim( z*cos(6*z), z*sin(6*z), seq(0,10, pi/64) ),
"3"=flight_sim( sin(z)*cos(20*z), sin(z)*sin(20*z), seq(0,pi,pi/399)),
"4"=custom())
head(x)
# x y z
# 1 0.00000000 0.00000000 0.00000000
# 2 0.04697370 0.01424932 0.04908739
# 3 0.08162934 0.05454298 0.09817477
# 4 0.09342212 0.11383519 0.14726216
# 5 0.07513972 0.18140332 0.19634954
# 6 0.02405703 0.24425508 0.24543693