function error: missing value where TRUE/FALSE needed cpos() (cwhmisc)

Question

This is my first post, I am quite new to R (one month) so I might have some really stupid mistake here.

I am trying to write a function to:

1. input the starting pattern and ending pattern
2. extract sub-string (in between the starting and ending pattern)
3. store the returned string value to a data frame

My sample string looks like this:

tweedehands?merkIds=9fdc7e2d-b40c-4ee6-896d-9f0453cb39c6&modelIds.9fdc7e2d-b40c-4ee6-896d-9f0453cb39c6=d56286d3-cecc-4183-9b6d-9c7e241de6c1&minimumprijs=5000&maximumprijs=6000&minimumbouwjaar=&maximumbouwjaar=&minimumkilometerstand=&maximumkilometerstand=&postcode=&afstand=

For example, I want to extract the value after minimumprijs= and before & , the function should return 5000

install.packages("cwhmisc")
library("cwhmisc")
getFilter <- function(x, STAchar = NA, ENDchar = "&"){
  x<- as.character(x)
  # pre-allocate a vector to store the extracted strings
  snippet = rep(0, length(x))
  for (i in 1:length(x))
   {#extract the initial position
      staPostion = (cpos(x[i], STAchar, 1) + nchar(STAchar))

    # extract the final position
      endPostion = (cpos(x[i], ENDchar, staPostion) - length(ENDchar))

    # extract the substring between the initial and final positions, inclusively
    snippet[i] = substr(x[i], staPostion, endPostion)
   }
  return(snippet)
}

However, this function is not working for me and I don't really understand what is the problem.

The error it returns is as follow:

Error in if (start + lsub1 > lstr) return(NA) else { : missing value where TRUE/FALSE needed Called from: cpos(x[i], ENDchar, staPostion) Browse[1]>

Now I can only think about to add some Error Handling, NA Handling lines inside of the function. But maybe it is something else.

Thanks for your help!!!

Answer 1

感谢您的所有帮助，但我刚刚发现使用 str_locate 和 substr 有一种更有效的方法来实现相同的功能