I Before E Except After C, R

Language: Layout:

words <- c('fiery', 'hierarchy', 'hieroglyphic', 'ceiling', 'inconceivable', 'receipt', 'daily', 'programmer', 'one', 'two', 'three', 'sleigh', 'stein', 'fahrenheit', 'deifies', 'either', 'nuclei', 'reimburse', 'ancient', 'juicier', 'societies', 'a', 'zombie', 'transceiver', 'veil', 'icier')

iBeforeE <- function(word) {
  isValid <- T

word <- tolower(word)
  letters <- unlist(strsplit(word, ''))
  
  # If "ei" appears in a word, it must immediately follow "c".
  indices <- unlist(gregexpr('ei', word))
  if (indices != -1) {
    for (index in indices) {
      if (index == 1 || letters[index - 1] != 'c') {
        isValid <- F
        break
      }
    }
  }
  
  # If "ie" appears in a word, it must not immediately follow "c".
  if (isValid) {
    indices <- unlist(gregexpr('ie', word))
    if (indices != -1) {
      for (index in indices) {
        if (index == 1 || (index > 0 && letters[index - 1] == 'c')) {
          isValid <- F
          break
        }
      }
    }
  }

isValid
}

# Check list of test words.
result <- sapply(words, function(word) {
  iBeforeE(word)
})
print(as.data.frame(result))

# Count word in enable1 word list that are exceptions to the rule.
words <- read.csv('https://norvig.com/ngrams/enable1.txt', header=F)
result <- sapply(words[,1], function(word) {
  iBeforeE(word)
})
count <- length(which(result == F))
print(count)

# Verify count is correct. The sum of the digits should add up to 18.
print(paste('Correct?', ifelse(sum(sapply(strsplit(as.character(count), ''), as.numeric)) == 18, 'Yes', 'No')))

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