CODEWITHSUNDEEP
r
Magnus Moller
Magnus Moller

Reputation: 87

Implementing in R the Epanechnikov kernel

I am trying to implement the Epanechnikov kernel. For that I wrote the following code:

epe<-function(x){if(abs(x)<1) {1-x^2}
  else {0}
}


epe(c(4,5,6,2,1,3))

epe_vec<-Vectorize(epe)

kern_epenechnikov_epe<-function(x, h, m = 512){
  rg <- range(x)
  xx <- seq(rg[1] - 3 * h, rg[2] + 3 * h, length.out = m)
  y <- numeric(m) 
  for (i in seq_along(xx))
    y[i] <-y[i] + epe_vec((xx[i] - x)/h))
  y <- 3*y / 4
  
  list(x = xx, y = y)
}

However, I am getting the following errors:

Error: object 'xx' not found } Error: unexpected '}' in "}"

xx is defined inside the function, I do not why R does not consider it.

I try the following implementation, it works:

kern_epenechnikov<-function(x, h, m = 512) {
  rg <- range(x)
  xx <- seq(rg[1] - 3 * h, rg[2] + 3 * h, length.out = m)
  y <- numeric(m) 
  for (i in seq_along(xx))
    y[i] <- y[i] + (1-((xx[i] - x)/h)^2)  
  y <- 3*y / 4
  
  list(x = xx, y = y)
}

In principal, the two implementations should be similar but they are not.

Question:

How do I solve the problem on the first implementation? How does the second compare to the first

Upvotes: 0

Views: 336

Answers (1)

scrameri
scrameri

Reputation: 707

It looks like a simple bracket error (you close an unopened bracket) in your first implementation.

The second example is equivalent, except that it doesn't contain a bracket error.

Can you try this? Note that I used curly brackets around the for loop, it's probably safer to use them, although they are not needed if there is only one statement in the loop.

kern_epenechnikov_epe<-function(x, h, m = 512) {
  rg <- range(x)
  xx <- seq(rg[1] - 3 * h, rg[2] + 3 * h, length.out = m)
  y <- numeric(m) 
  for (i in seq_along(xx)) {
    y[i] <-y[i] + epe_vec((xx[i] - x)/h) # remove second ')'
  }
  y <- 3*y / 4


  list(x = xx, y = y)
}

By the way, such bracket errors are quickly spotted if you use curly brackets around the for loop and RStudio.

Upvotes: 2

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