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/*
 * Copyright (c) 2010-2021 Haifeng Li. All rights reserved.
 *
 * Smile is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Smile is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Smile.  If not, see .
 */
 
package smile.math

/** Distance functions.
 *
 * @author Beck Gaël
 */
package object distance {

  /**
   * Build the contingency matrix (a, b, c, d) where for each bite i, j of vector 1 and 2 :
   *   - a is incremented if i = 1, j = 1
   *   - b is incremented if i = 1, j = 0
   *   - c is incremented if i = 0, j = 1
   *   - d is incremented if i = 0, j = 0
   */
  def contingency(x: Array[Int], y: Array[Int]): (Int, Int, Int, Int) = {
    require(x.length == y.length, "Arrays have different length")

    var (a,b,c,d) = (0, 0, 0, 0)

    x.zip(y).foreach {
      case (1, 1) => a += 1
      case (1, 0) => b += 1
      case (0, 1) => c += 1
      case (0, 0) => d += 1
      case (x, y) => throw new IllegalArgumentException("Invalid value ($x, $y)")
    }

    (a, b, c, d)
  }
}