Letter Frequency

Letter Frequency is a ShinyApp that calculates the frequency that every letter appears in a sample of writing and compares the results graphically to the letter frequencies of the English language or Shakepeare's writing.

This ShinyApp is a fun way of comparing samples of writing from different authors or trying to tackle texts encrypted with a substitution cypher. It can also be used to compare letter frequencies of other languages with English.

You can find Letter Frequency at https://kamerlingh.shinyapps.io/dataproducts.

Identifying Authors

Authors use a distinct mix of letters, leading to unique letter frequency “signatures”, which means letter frequency can be used as evidence of a work’s authenticity.

If someone claimed that they found a previously undiscovered play and attributed it to Shakespeare, but the letter frequency of this play did not match that of Shakespeare’s other work, we should be skeptical of this claim.

Cryptography

The letter frequency of a text that has been encrypted with a substition cypher can be analyzed to figure out the cypher.

In a simple substitution cypher, every letter of a text is changed into a another letter. For example, all A’s in the unencrypted text might be changed to T’s in the encrypted text.

library(stringr)
abc = c("e","t","a","o","i","n","s","h","r","d","l","c",
        "u","m","w","f","g","y","p","b","v","k","j","x","q","z")
English = c(12.702, 9.056, 8.167, 7.507, 6.966, 6.749, 6.327, 6.094, 5.987,
            4.253, 4.025, 2.782, 2.758, 2.406, 2.361, 2.228, 2.015, 1.974,
            1.929, 1.492, 0.978, 0.772, 0.153, 0.15, 0.095, 0.074)

lettercount <- function(text){
    text <- tolower(text)
    length <- str_length(text)
    freq <- as.data.frame(rep(0,26))

    count_char <- function(letter,some_text){
        str_count(some_text,letter)*100/length
    }

    #Calculate the frequency of each letter in the text.
    freq <- apply(as.data.frame(abc),1,count_char,some_text=text)

    #Return a table with the calculated frequencies and those of English.
    t(as.data.frame(cbind(English,freq)))
}