storing the function output to an object in R

Question

I have a dataframe.

structure(list(CONTENT = c("@_ShankarNath Hey Shankar, thank you for highlighting this to us, it will be taken care.", 
"#deals #Puma Cell Kilter Black Sneakers is selling cheaper at INR 3899 today https://t.co/n9wLwofVzz #jabong"
), MEDIA_PROVIDER = c("TWITTER", "TWITTER")), .Names = c("CONTENT", 
"MEDIA_PROVIDER"), class = "data.frame", row.names = 1:2)

I have an input text file and an output text file. Input file has a field named "CONTENT". From the data frame given above I am passing the sentence through a loop and performing some calculations. In the output file I have a field named "Score", where the a score will be populated. I have to extract the score and store it in an object.

I have written the following codes.

sco <- for (i in 1:nrow(dfa)){
  s <- list()
  filecon <- file("input.txt")
  writeLines(c("Username = ABC","Password = 123",paste("Content = ", dfa$CONTENT[i]),"Delimiter =  "), filecon)
  close(filecon)

# perform all the calculations

  a <- readLines("output.txt")
  get.score <- function(scor) {
    score <- scor[grepl("Score = ", scor)]
      as.numeric(strsplit(score, "Score = ")[[1]][2])
  }
  s <- get.score(a)
  print(s)
  }

The output file looks like this:

c("Content = @_ShankarNath Hey Shankar, thank you for highlighting this to us, it will be taken care.", 
"Delimiter =  ", "Score = 1.978", "Result = Success")

The value of the score get replaced with every iteration, and I am trying to capture the same, before the loop moves on to the second line.

The print score return the values for all the statements. However when I try replacing the print(s) with s the function is returning NULL. I tried using return(s) I am getting an error Error: No function to return from, jumping to the top level.

Not sure where I am going wrong.

@mtoto since for every input that I provide I get an output generated and pasted. If i dont capture the output and store it, the loop moves on to the second line and I will have a new output where the old output gets replaced. Hence, I thought I should define the function inside the loop itself. — Apricot
– Apricot, Commented Feb 17, 2016 at 6:59
@mtoto the print function prints the output on to the screen for every input iterated by the loop — Apricot
– Apricot, Commented Feb 17, 2016 at 7:00
Maybe s[i] <- get.score(a), and keep s <- list() outside the for loop ? — zx8754
– zx8754, Commented Feb 17, 2016 at 7:07
you script is wired because ` for` doesn't output anything so ` sco <- for(i in ...` doesn't make any sense — ClementWalter
– ClementWalter, Commented Feb 17, 2016 at 8:15

ClementWalter · Accepted Answer · 2016-02-17 10:50:17Z

1

Without testing it so far, I suggest two alternatives, either using apply or foreach from package foreach as it seems what you would like to write.

get.score <- function(scor) {
    score <- scor[grepl("Score = ", scor)]
    as.numeric(strsplit(score, "Score = ")[[1]][2])
}

sco <- apply(dfa, 1, function(v) {
             filecon <- file("input.txt")
             writeLines(c("Username = ABC","Password = 123",paste("Content = ", v['CONTENT']),"Delimiter =  "), filecon)
             close(filecon)

             # perform all the calculations
             a <- readLines("output.txt")
             get.score(a)
})

This will output a matrix or vector, but depending on the output of get.score this might not be suitable. You can also use lapply

sco <- lapply(dfa$CONTENT, function(v) {
             filecon <- file("input.txt")
             writeLines(c("Username = ABC","Password = 123",paste("Content = ", v),"Delimiter =  "), filecon)
             close(filecon)

             # perform all the calculations
             a <- readLines("output.txt")
             get.score(a)
})

Finally it the for structure is more familiar to you, you can try

library(foreach)
sco <- foreach(v=dfa$CONTENT) %do% {
             filecon <- file("input.txt")
             writeLines(c("Username = ABC","Password = 123",paste("Content = ", v),"Delimiter =  "), filecon)
             close(filecon)

             # perform all the calculations
             a <- readLines("output.txt")
             get.score(a)
}

Not that the foreach package allows you to make parallel computation.

edited Feb 17, 2016 at 10:50

answered Feb 17, 2016 at 8:28

ClementWalter

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2 Comments

Apricot Over a year ago

Many many thanks....was struggling with this since yesterday evening...i did use apply...but within for loop. Your first option with apply worked. I was under the impression, that since i have to iterate over each line probably the for loop is best suited. Many thanks again.

ClementWalter Over a year ago

the second should work also now, previously I left ,1 , in the lapply from copy/paste of the apply case

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