Question

For a dataset of "Baltimore homicides"
It is required to create a function that takes a string for example "shooting" and return an integer represents the count of victims of "shooting".
I wrote the following function but i receive errors

Error: unexpected ‘}’ in " }"

Error: object ‘counti’ not found

I also cant figure out if the ==Null is correct

count <- function(cause = NULL) {

## Check that "cause" is non-NULL; else throw error
if cause==NULL
{
stop()
print("no cause provided")
}

## Read "homicides.txt" data file
homicides <- readLines("homicides.txt")
## Extract causes of death
i <- grep(cause, homicides)  ##get indices of cause
counti <- lenghth(i) ##get count of indices
## Check that specific "cause" is allowed; else throw error
if counti=0
{
stop()
print("no such cause")
}

## Return integer containing count of homicides for that cause      
return(counti)  
}

---

this is my working function after edit, thanks guys

count <- function(cause = NULL) {
  if(missing(cause) | is.null(cause)) stop("no cause provided")
  homicides <- readLines("homicides.txt")
  i=length(grep(cause, homicides))
  if(i==0) stop("no cause found")
  return(i)
  }

Answer 1

You can simplify your function to 2 lines by doing this:

count <- function(cause = NULL, data) {
  if(is.null(cause)) stop("no cause provided")
  length(grep(cause, data))
}

data <- c("murder", "some other cause")

count("murder", data)
[1] 1

Note the following principles:

• R has many features of a functional language. This means that each function should, as far as possible, depend only on the arguments you pass it.
• When you have a bug in your code, simplify it to the shortest possible version, fix the bug, then build out from there.

Also, keep stop() for really fatal errors. Not finding a search string in your data isn’t an error, it simply means the cause wasn’t found. You don’t want your code to stop. At most, issue a message() or a warning().