Creating Subset of Vector Adds Null Values - r

Question

I'm trying to create a mergeSort algorithm in R. While I think I have the method down, the first time I create the vector e, I end up with a vector of length 4 instead of 2. This causes the error below:
"Error in if (a[2] < a[1]) { : missing value where TRUE/FALSE needed"
For some reason, R is adding an extra 2 elements to what should be a two-element vector. If anyone has an explanation for this, that would be wonderful. (Please limit advice to solving this error. I want to figure out how to do the rest on my own.)
Code:
addLeftOver <- function(buffer, array, index) {
j <- length(buffer)
for(i in array[index:length(array)]) {
buffer[j] = i
print(i)
j <- j+1
}
return(buffer)
}
mergeSort <- function(a) {
len <- length(a)
print(a)
print(len)
browser()
if(len<=2) { #base case
if(len==1) {
return(a)
}
if(a[2]<a[1]) {
return(c(a[2],a[1]))
}
return(a)
}
print(len/2)
b <- mergeSort(a[1:(len/2)]) #recursion
e <- mergeSort(a[(len/2)+1:len]) #recursion
indexB <- 1
indexE <- 1
buffer
for(i in 1:len) {
if(e[indexC]<b[indexB]) {
buffer[index] <- e[indexE]
index <- index + 1
indexE <- indexE + 1
} else {
buffer[index] <- b[indexB]
index <- index + 1
indexB <- indexB + 1
}
if(indexB==len/2) {
buffer = addLeftover(buffer, e, indexE)
return(buffer)
}
if(indexE==len/2) {
buffer = addLeftover(buffer, b, indexB)
return(buffer)
}
}
}
sumArray <- c(6,4,2,7,8,1,3,5)
print(mergeSort(sumArray))
The addLeftOver() function's purpose is to copy the remnants of one of the two vectors (b or e) to the buffer when the end of the other has been reached.

Answer 1

Main error can be fixed with parenthesis. e <- mergeSort(a[(len/2)+1:len]) should be e <- mergeSort(a[((len/2)+1:len])
That and some other bugs were fixed.
Working code:
addLeftOver <- function(buffer, array, index)
{
j <- length(buffer)+1
for(i in array[index:length(array)]) {
buffer[j] = i
j <- j+1
}
return(buffer)
}
mergeSort <- function(a)
{
len <- length(a)
if(len<=2)
{
if(len==1)
{
return(a)
}
if(a[2]<a[1])
{
return(c(a[2],a[1]))
}
return(a)
}
half <- as.integer(len/2)
b <- mergeSort(a[1:(half)])
e <- mergeSort(a[((half)+1):len])
index <- 1
indexB <- 1
indexE <- 1
buffer <- c(0)
for(i in 1:len)
{
if(e[indexE]<b[indexB])
{
buffer[index] <- e[indexE]
index <- index + 1
indexE <- indexE + 1
}
else
{
buffer[index] <- b[indexB]
index <- index + 1
indexB <- indexB + 1
}
if(indexB==(length(b))+1)
{
buffer = addLeftover(buffer, e, indexE)
return(buffer)
}
if(indexE==(length(e))+1)
{
buffer = addLeftover(buffer, b, indexB)
return(buffer)
}
}
}