How to plot a function curve in R - r

Question

What are the alternatives for drawing a simple curve for a function like
eq = function(x){x*x}
in R?
It sounds such an obvious question, but I could only find these related questions on stackoverflow, but they are all more specific
Plot line function in R
Plotting functions on top of datapoints in R
How can I plot a function in R with complex numbers?
How to plot a simple piecewise linear function?
Draw more than one function curves in the same plot
I hope I didn't write a duplicate question.

Answer 1

I did some searching on the web, and this are some ways that I found:
The easiest way is using curve without predefined function
curve(x^2, from=1, to=50, , xlab="x", ylab="y")
You can also use curve when you have a predfined function
eq = function(x){x*x}
curve(eq, from=1, to=50, xlab="x", ylab="y")
If you want to use ggplot,
library("ggplot2")
eq = function(x){x*x}
ggplot(data.frame(x=c(1, 50)), aes(x=x)) +
stat_function(fun=eq)

Answer 2

You mean like this?
> eq = function(x){x*x}
> plot(eq(1:1000), type='l')
(Or whatever range of values is relevant to your function)

Answer 3

plot has a plot.function method
plot(eq, 1, 1000)
Or
curve(eq, 1, 1000)

Answer 4

Here is a lattice version:
library(lattice)
eq<-function(x) {x*x}
X<-1:1000
xyplot(eq(X)~X,type="l")

Answer 5

Lattice solution with additional settings which I needed:
library(lattice)
distribution<-function(x) {2^(-x*2)}
X<-seq(0,10,0.00001)
xyplot(distribution(X)~X,type="l", col = rgb(red = 255, green = 90, blue = 0, maxColorValue = 255), cex.lab = 3.5, cex.axis = 3.5, lwd=2 )
If you need your range of values for x plotted in increments different from 1, e.g. 0.00001 you can use:
X<-seq(0,10,0.00001)
You can change the colour of your line by defining a rgb value:
col = rgb(red = 255, green = 90, blue = 0, maxColorValue = 255)
You can change the width of the plotted line by setting:
lwd = 2
You can change the size of the labels by scaling them:
cex.lab = 3.5, cex.axis = 3.5

Answer 6

As sjdh also mentioned, ggplot2 comes to the rescue. A more intuitive way without making a dummy data set is to use xlim:
library(ggplot2)
eq <- function(x){sin(x)}
base <- ggplot() + xlim(0, 30)
base + geom_function(fun=eq)
Additionally, for a smoother graph we can set the number of points over which the graph is interpolated using n:
base + geom_function(fun=eq, n=10000)

Answer 7

Function containing parameters
I had a function (emax()) involving 3 parameters (a, b & h) whose line I wanted to plot:
emax = function(x, a, b, h){
(a * x^h)/(b + x^h)
}
curve(emax, from = 1, to = 40, n=40 a = 1, b = 2, h = 3)
which errored with Error in emax(x) : argument "a" is missing, with no default error.
This is fixed by putting the named arguments within the function using this syntax:
curve(emax(x, a = 1, b = 2, h = 3), from = 1, to = 40, n = 40)
which is contrary to the documentation which writes curve(expr, from, to, n, ...) rather than curve(expr(x,...), from, to, n).