CISC181 S2017 Lab8

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Preliminaries

  • Make a new project with n = 8 (following these instructions)
  • Name your main class "Lab8" (when creating a new module in the instructions above, in the Java class name field)
  • Modify Lab8.java by adding your name and section number in a comment before the Lab8 class body.

Instructions

In this lab you will analyze text files by breaking them into n-grams at the character level, and use those n-grams to generate random text in the same "style" (in a statistical sense). An n-gram is a sequence of n consecutive characters from the input. The complete set of n-grams for a text overlap each other--for example, if the text is "the three pirates ate their pie", the 2-grams are listed below:

2-gram Characters after 2-gram Characters after 2-gram Characters after
"th" "e", "r", "e" "ra"
"he" "at"
"e " "te"
" t" "es"
"hr" "s "
"re" " a"
"ee" " t"
" p" "ei"
"pi" "r "
"ir" "ie"

Your job is to find all of the n-grams for a text, and furthermore to record all of the possible characters that follow each particular n-gram. In the "woodchucks" example, no 3-grams are repeated, but suppose you look at 1-grams. Then the set of characters is "w", "o", "d", "c", "h", "u", "k", and "s". "o" is followed by an "o" once, and a "d" once. "c" is followed by an "h" once and a "k" once.

Suppose, for example, that you are working with 2-grams, and you have found that 80% of the time "th" is followed by "e ", 10% by "is", 7% by "at", and 3% by "es". Then, when you are generating text, after you have generated "th" you should randomly choose "e " with probability 0.8, "is" with probability 0.1, "at" with probability 0.07, and "es" with probability 0.03.

RandomWriter

You are to implement a Java public class RandomWriter that provides a random writing application. Your class should have a two-argument constructor that takes:

  • String source: The name of an input file to read and analyze
  • int n: A non-negative number indicating the length of each "gram," or character sequence, to break the file into

and also a method generateText() that takes the following two parameters:

  • int length: A non-negative number of characters to generate.
  • String result: The name of the output file

Testing

In main(), run your code on the following files:

Generate approximately 500 characters of text for each input. Print the text in reasonable length lines, breaking only at spaces (not in the middle of a word). Do this for 1-grams, 2-grams, 4-grams, and 6-grams.

Acknowledgments

This assignment is shamelessly copied from one created by David Matuszek at the University of Pennsylvania.