How to return a value from an R function with Control Structure

Question

I'm trying to extract the rating from a column inside a DataFrame. I have written the below function. However, the function would not stop executing and the column does not get updated.

Column values are string for example;

• Rating R violence sexual content language
• Rating PG-13 content language
• ""

Desired output:

• if the row value of the column is "" or empty than the new value should be NA
• if the row value of the column is Rating R violence sexual content language, than the new value should be "R"

• if the row value of the column is Rating PG-13 content language, than the new value should be "PG-13"

  C <- function (column) 
  {
    len <- length(DF$column)
  
    for (i in 1:len) 
  
    {
      a <- DF$column[i]
      b <-  unlist(strsplit(a," "))
  
    if ( length(b) == 0 ) 
    {
  
      x <-  NA
  
      DF$column[i] <- x
  
     } else ( b[1] == "Rating" & length(b) > 0 ) 
  
     DF$column[i] <- mpaaRating[2]
  
  
    } 
  }  
  
  
  DF$mpaa <- CleanMpaa(DF$mpaa)
  

Thank you

Answer 1

只需使用嵌套的ifelse即可。不需要循环：

DF <- data.frame(list(mpaa=c("Rating R", "Rating PG-13", "", "PG")), 
                 stringsAsFactors = FALSE)
DF
#           mpaa
# 1     Rating R
# 2 Rating PG-13
# 3              
# 4           PG

DF$clean_mpaa <- ifelse(nchar(DF$mpaa) == 0, NA, 
                        ifelse(grepl("Rating", DF$mpaa),          # FINDS PATTERN
                               gsub("Rating ", "", DF$mpaa),      # REPLACES PATTERN
                               DF$mpaa))
#           mpaa clean_mpaa
# 1     Rating R          R
# 2 Rating PG-13      PG-13
# 3                    <NA>
# 4           PG         PG