old_contents: import numpy
  
  from chainer import cuda
  from chainer import function
  from chainer.utils import type_check
  
  
  class BinaryAccuracy(function.Function):
  
      ignore_label = -1
  
      def check_type_forward(self, in_types):
          type_check.expect(in_types.size() == 2)
          x_type, t_type = in_types
  
          type_check.expect(
              x_type.dtype == numpy.float32,
              t_type.dtype == numpy.int32,
              t_type.shape == x_type.shape,
          )
  
      def forward(self, inputs):
          xp = cuda.get_array_module(*inputs)
          y, t = inputs
          # flatten
          y = y.ravel()
          t = t.ravel()
          c = (y >= 0)
          count = (t != self.ignore_label).sum()
          if int(count) == 0:
              count = 1
          return xp.asarray((c == t).sum(dtype='f') / count, dtype='f'),
  
  
  def binary_accuracy(y, t):
      """Computes binary classification accuracy of the minibatch.
  
      Args:
          y (Variable): Variable holding a matrix whose i-th element
              indicates the score of positive at the i-th example.
          t (Variable): Variable holding an int32 vector of groundtruth labels.
              If ``t[i] == -1``, correspondig ``x[i]`` is ignored.
              Accuracy is zero if all groundtruth labels are ``-1``.
  
      Returns:
          Variable: A variable holding a scalar array of the accuracy.
  
      .. note:: This function is non-differentiable.
  
      """
      return BinaryAccuracy()(y, t)
  
new_contents: import numpy
  
  from chainer import cuda
  from chainer import function
  from chainer.utils import type_check
  
  
  class BinaryAccuracy(function.Function):
  
      ignore_label = -1
  
      def check_type_forward(self, in_types):
          type_check.expect(in_types.size() == 2)
          x_type, t_type = in_types
  
          type_check.expect(
              x_type.dtype == numpy.float32,
              t_type.dtype == numpy.int32,
              t_type.shape == x_type.shape,
          )
  
      def forward(self, inputs):
          xp = cuda.get_array_module(*inputs)
          y, t = inputs
          # flatten
          y = y.ravel()
          t = t.ravel()
          c = (y >= 0)
          count = xp.maximum(1, (t != self.ignore_label).sum())
          return xp.asarray((c == t).sum(dtype='f') / count, dtype='f'),
  
  
  def binary_accuracy(y, t):
      """Computes binary classification accuracy of the minibatch.
  
      Args:
          y (Variable): Variable holding a matrix whose i-th element
              indicates the score of positive at the i-th example.
          t (Variable): Variable holding an int32 vector of groundtruth labels.
              If ``t[i] == -1``, correspondig ``x[i]`` is ignored.
              Accuracy is zero if all groundtruth labels are ``-1``.
  
      Returns:
          Variable: A variable holding a scalar array of the accuracy.
  
      .. note:: This function is non-differentiable.
  
      """
      return BinaryAccuracy()(y, t)
  
subject: Use maximum instead of if-statement