Curve Fitting in R

Question

Any resources for curve fitting in R? I came across https://systatsoftware.com/products/sigmaplot/product-uses/sigmaplot-products-uses-curve-fitting-using-sigmaplot/

Any similar recommendations or libraries in R?

Thank you!

Answer 1

Hi There are not one but several ways to do curve fitting in R. You could start with something as simple as below

x <- c(32,64,96,118,126,144,152.5,158)
#make y as response variable
y <- c(99.5,104.8,108.5,100,86,64,35.3,15)    
plot(x,y,pch=19)

This should give you the below plot. Eyeballing the curve tells us we can fit some nice polynomial curve here.

Now we could fit our curve(s) on the data below:

linMod  <- lm(y~x)
#second degree polynomial model
linMod2 <- lm(y~poly(x,2,raw=TRUE))
#third degree polynomial model
linMod3 <- lm(y~poly(x,3,raw=TRUE))
#fourth degree polynomial model
linMod4 <- lm(y~poly(x,4,raw=TRUE))
#generate new data in range of 50 numbers starting from 30 and ending at 160
newData <- seq(30,160, length=50)
plot(x,y,pch=19,ylim=c(0,150))
lines(newData, predict(linMod, data.frame(x=newData)), col="red")
lines(newData, predict(linMod2, data.frame(x=newData)), col="green")
lines(newData, predict(linMod3, data.frame(x=newData)), col="blue")
lines(newData, predict(linMod4, data.frame(x=newData)), col="purple")

Giving us:

This is just a simple illustration of curve fitting in R. There are tons of tutorials available out there, perhaps you could start looking here:

• http://www.css.cornell.edu/faculty/dgr2/teach/R/R_CurveFit.pdf
• https://rpubs.com/carlmart/228874
• Fitting a curve to specific data