Plotting functions of functions

Question

So I'm kind of new to R, and I need to plot some functions. My understanding of curve in R is that it requires a function that has x as its single input. Since my functions are all just different representations of the same main function, I first thought I would create the main function, and then I would define each specific function individually.

# The principal function
puiss <- function(theta, inf, sup) {
  for(k in inf:sup) {
    total += (choose(30,k) * (theta^k) * ((1-theta)^(30-k)))
  }
}

# The specific functions I need to draw on the same plot
p1 <- function(x) { puiss(x,2,13) }
p2 <- function(x) { puiss(x,3,14) }
p3 <- function(x) { puiss(x,3,13) }

# Can't even get to trace just a single one... :'(
curve(p1,
0, 1,                              # from 0 to 1
main="puissance(theta)",           # title
xlab="x", ylab="theta")            # axes

curve(p2, add=T)                   # adding the other function
curve(p3, add=T)                   # adding the other function

I get this error:

'expr' did not evaluate to an object of length 'n'

I've tried multiple approaches, but this one seemed to be the closest one to what it should have been.

Among other alternatives, I've tried:

changing from <- to = for the specific functions
using no {} (brackets) for the specific functions
plugging the for loop directly into the curve and replacing theta by x and inf:sup appropriately
trying to use p1(x) inside curve
I've also read that some times Vectorize() is needed, so I've tried Vectorize(p1) inside curve

What am I doing wrong?

It might help to disclose that my main function is just a Binomial(30, theta)'s mass function (probability) evaluated in different regions (the summation within the boundaries, my sigma which is a for loop because I couldn't figure out how to properly create a sigma function in R). In other words, it is a cumulative distribution function.

Ultimately, I'm trying to plot the 3 specific functions together on the same plot.

Thanks for the help! :)

bobbel · Accepted Answer · 2018-11-27 21:19:02Z

1

It seems you are using some Python (or similar) code in your function definition. Here is the R version of it, which for me will plot the results when calling curve.

puiss <- function(theta, inf, sup) {
  total = 0
  for(k in inf:sup) {
    # "+=" does not work for R
    total <- total + (choose(30,k) * (theta^k) * ((1-theta)^(30-k)))
  }
  # you need to use parentheses around total
  return(total)
}

answered Nov 27, 2018 at 21:19

bobbel

2,0499 silver badges23 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

payne Over a year ago

Thank you so much! I've reverted the question back to its initial state so that your answer makes more sense. Maybe mention the fact that I didn't even have a return. That's embarrassing. (However, I was indeed coding in NotePad, which might not have been a good idea.)

MrFlick Over a year ago

A loop isn't even necessary in R. You can just do puiss <- function(theta, inf, sup) {k <- inf:sup; sum(choose(30,k) * (theta^k) * ((1-theta)^(30-k)))}. An explicit return() is not required.

payne Over a year ago

@MrFlick how could I add a legend of the three functions plotted so as to know which is which ? I've added colors, but it still doesn't identify the functions.

bobbel Over a year ago

True, I wasn't quite focused on improving the function, but merely on making it work.

MrFlick Over a year ago

It's pretty straightforward to add a legend: stackoverflow.com/questions/46186850/adding-a-legend-to-a-plot

Collectives™ on Stack Overflow

Plotting functions of functions

1 Answer 1

5 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related