How to remove non-alphabetic characters and convert all letter to lowercase in R?

Question

In the following string:

"I may opt for a yam for Amy, May, and Tommy."

How to remove non-alphabetic characters and convert all letter to lowercase and sort the letters within each word in R?

Meanwhile, I try to sort words in sentence and removes the duplicates.

Answer 1

You could use stringi

library(stringi)
unique(stri_sort(stri_trans_tolower(stri_extract_all_words(txt, simplify = TRUE))))

Which gives:

## [1] "a"     "amy"   "and"   "for"   "i"     "may"   "opt"   "tommy" "yam" 

Update

As per mentionned by @DavidArenburg, I overlooked the "sort the letters within words" part of your question. You didn't provide a desired output and no immediate application comes to mind but, assuming you want to identify which words have a matching counterpart (string distance of 0):

unique(stri_sort(stri_trans_tolower(stri_extract_all_words(txt, simplify = TRUE)))) %>%
  stringdistmatrix(., ., useNames = "strings", method = "qgram") %>%

#       a amy and for i may opt tommy yam
# a     0   2   2   4 2   2   4     6   2
# amy   2   0   4   6 4   0   6     4   0
# and   2   4   0   6 4   4   6     8   4
# for   4   6   6   0 4   6   4     6   6
# i     2   4   4   4 0   4   4     6   4
# may   2   0   4   6 4   0   6     4   0
# opt   4   6   6   4 4   6   0     4   6
# tommy 6   4   8   6 6   4   4     0   4
# yam   2   0   4   6 4   0   6     4   0

  apply(., 1, function(x) sum(x == 0, na.rm=TRUE)) 

# a   amy   and   for     i   may   opt tommy   yam 
# 1     3     1     1     1     3     1     1     3 

Words with more than one 0 per row ("amy", "may", "yam") have a scrambled counterpart.

Answer 2

str <- "I may opt for a yam for Amy, May, and Tommy."

## Clean the words (just keep letters and convert to lowercase)
words <- strsplit(tolower(gsub("[^A-Za-z ]", "", str)), " ")[[1]]

## split the words into characters and sort them
sortedWords <- sapply(words, function(word) sort(unlist(strsplit(word, ""))))

## Join the sorted letters back together
sapply(sortedWords, paste, collapse="")

# i     may     opt     for       a     yam     for     amy     may     and 
# "i"   "amy"   "opt"   "for"     "a"   "amy"   "for"   "amy"   "amy"   "adn" 
# tommy 
# "mmoty" 

## If you want to convert result back to string
do.call(paste, lapply(sortedWords, paste, collapse=""))
# [1] "i amy opt for a amy for amy amy adn mmoty"