R function doesn't loop through column but repeats first row result

Question

I am trying to use the stemming function suggested in the corpus package stemming vignette here https://cran.r-project.org/web/packages/corpus/vignettes/stemmer.html

but when I try to run the function on the entire column it seems to just be repeating the result for the first row down the rest of the rows. I'm guessing this has to do with the [[1]] within the following function. I'm guessing the solution is something along the lines of "for i in x" but I'm not familiar enough with writing functions to know how to solve this.

df <- data.frame(x = 1:7, y= c("love", "lover", "lovely", "base", "snoop", "dawg", "pound"), stringsAsFactors=FALSE)

stem_hunspell <- function(term) {
    # look up the term in the dictionary
    stems <- hunspell::hunspell_stem(term)[[1]]

    if (length(stems) == 0) { # if there are no stems, use the original term
        stem <- term
    } else { # if there are multiple stems, use the last one
        stem <- stems[[length(stems)]]
    }

    stem
}

df[3] <- stem_hunspell(df$y)

Try returning `stem[[1]]` as last line in function to get the underlying vector in that one-item list. — Parfait, Nov 06 '19 at 20:49

score 1 · Accepted Answer · answered Nov 06 '19 at 20:52

Your intuition is right.

hunspell_stem(term) returns a list of length length(term) of character vectors.

The vectors seem to have the word but only if it was found in a dictionary as the first element and the stem as the second if it isn't a stem already.

> hunspell::hunspell_stem(df$y)
[[1]]
[1] "love"

[[2]]
[1] "lover" "love" 

[[3]]
[1] "lovely" "love"  

[[4]]
[1] "base"

[[5]]
[1] "snoop"

[[6]]
character(0)

[[7]]
[1] "pound"

The below function returns either the stem or the original term

stem_hunspell <- function(term) {
  stems <- hunspell::hunspell_stem(term)
  output <- character(length(term))

  for (i in seq_along(term)) {
    stem <- stems[[i]]
    if (length(stem) == 0) {
      output[i] <- term[i]
    } else {
      output[i] <- stem[length(stem)]
    }
  }
  return(output)
}

If you want dawg not to be returned the function becomes simpler:

stem_hunspell <- function(term) {
  stems <- hunspell::hunspell_stem(term)
  output <- character(length(term))

  for (i in seq_along(term)) {
    stem <- stems[[i]]
    if (length(stem) > 0) {
      output[i] <- stem[length(stem)]
    }
  }
  return(output)
}

Wonderful, thanks so much for your time. I definitely want to keep words not found in the dictionary (e.g. slang - I am using twitter data) so that was a happy accident including that word in my example. — Kreitzbe87, Nov 07 '19 at 03:30
Glad I could help. If this solved your problem please mark the answer as accepted so others with the same issue can see there's a solution — Robin Gertenbach, Nov 07 '19 at 06:10

R function doesn't loop through column but repeats first row result

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