Fitting a function in R

Question

I have a few datapoints (x and y) that seem to have a logarithmic relationship.

> mydata
    x   y
1   0 123
2   2 116
3   4 113
4  15 100
5  48  87
6  75  84         


        

Answer 1

Maybe using a cubic specification for your model and estimating via lm would give you a good fit.

# Importing your data
dataset <- read.table(text='
    x   y
1   0 123
2   2 116
3   4 113
4  15 100
5  48  87
6  75  84
7 122  77', header=T)

# I think one possible specification would be a cubic linear model
y.hat <- predict(lm(y~x+I(x^2)+I(x^3), data=dataset)) # estimating the model and obtaining the fitted values from the model

qplot(x, y, data=dataset, geom="line") # your plot black lines
last_plot() + geom_line(aes(x=x, y=y.hat), col=2) # the fitted values red lines

# It fits good.