How to plot a function curve in 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 )

1. If you need your range of values for x plotted in increments different from 1, eg 0.00001 you can use:

X<-seq(0,10,0.00001)

2. You can change the colour of your line by defining a rgb value:

col = rgb(red = 255, green = 90, blue = 0, maxColorValue = 255)

3. You can change the width of the plotted line by setting:

lwd = 2

4. 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) .