language.cpp

#include "language.h"
#include <fstream>
#include <cmath>

// default Constructor
LANG::LANG() {
  txt = ""; // Initialize global text variable to empty value
  std::vector<int> frequencies;
}

// loads a LANG object's text data to 'txt', given a file 'infile'
LANG::LANG(std::ifstream &infile) {

  std::string line;
  std::string text;

  // check if the file is accessible
  if (infile.fail()) {
    std::runtime_error("ERROR: File could not be opened");
  } else {
    while (getline(infile, line)) {
      // adds line to full sequence
      text+=line;
    }
  }
  infile.close();

  // tests to see if file text language data is valid format
  // if `text` contains invalid characters, throws a std::runtime_error
  for (unsigned long i = 0; i < text.size(); i++) {
    if (text[i] != '\n' && text[i] != ' ' && (text[i] < 'a' || text[i] > 'z')) {
      throw std::runtime_error("ERROR: Invalid text input, must only contain lowercase letters and spaces");
      }
  }
  txt = text; // Initialize global text variable
}

// getter for language text data
std::string LANG::getText() {
  return txt;
}
// getter for frequency profile
std::vector<int> LANG::getFrequency() {
  return frequencies;
}

/*
get a frequency profile
    - takes string of language data from a LANG object and starting at first index, increments by one while finding the trigram value for every 3 characters
    - add one to the frequency counter vector at that trigram value index
*/
void LANG::calcFrequency() {
  // get language text
  std::string text = this->getText();

  // initialize frequencies vector to 19683 zeroes
  std::vector<int> tempFreq(19683);
    // iterate through text input,
    for (unsigned long i = 0; i < text.size()-2; i++)
    {
      // initialize variables for letters in the trigram
      char letter1 = text[i];
      char letter2 = text[i+1];
      char letter3 = text[i+2];
      // check if the trigram contains a newline character, and if so skip over it
      if (letter1 =='\n') continue;
      else if (letter2 =='\n') {
        letter2 = text[i+2];
        letter3 = text[i+3];
      }
      else if (letter3 =='\n') {
        letter3 = text[i+3];
      }

      // get the value of each letter
      int a = letter1 - 'a' + 1;
      int b = letter2 - 'a' + 1;
      int c = letter3 - 'a' + 1;

      // check if trigram contains spaces
      if (letter1 == ' ') a = 0;
      if (letter2 == ' ') b = 0;
      if (letter3 == ' ') c = 0;
      // find the index of the trigram by using the formula and add 1 to its index
      int index = ((a*(27*27)) + (b*27) + c);
      tempFreq[index]+=1;
      }
      // initialize global frequencies variable
      frequencies = tempFreq;
}

// implementation of cosine similarity function, called on a LANG object and takes training file vector as input parameter
double LANG::calcSimilarity(std::vector<int> teFile) {
  // calculate and get frequency profile for training file
  this->calcFrequency();
  std::vector<int> trFile = this->getFrequency();
  unsigned long long numerator = 0;
  unsigned long long denom1 = 0;
  unsigned long long denom2 = 0;
  for (int i=0; i<=19682; i++) {
    numerator += (trFile[i]*teFile[i]);
    denom1 += (trFile[i]*trFile[i]);
    denom2 += (teFile[i]*teFile[i]);
  }
  double denom = std::sqrt(denom1)*std::sqrt(denom2);
  double similarity = std::abs(numerator/denom);
  return similarity;
}