Question

与Array#pop()类似，我想创建一个删除矩阵最后一列的破坏性方法：Matrix#hpop()（h代表水平）。

如何使此方法具有破坏性？没有像Matrix#replace()这样的方法可以用来修改对象的内部状态。

  # Removes trailing columns from a Matrix.
  # @param number_of_columns [Integer] number of trailing columns to be removed
  # @return [Matrix] matrix
  # @raise [ErrDimensionMismatch] if Matrix does not have enough columns for operation
  def hpop(number_of_columns = 1)        
    Matrix.Raise ErrDimensionMismatch unless number_of_columns < self.column_count

    columns = []
    last_column_to_be_included = self.column_count - number_of_columns
    self.column_vectors.each_with_index do |column, index|
      break if index + 1 > last_column_to_be_included
      columns << column.to_a
    end

    Matrix.columns(columns) # should be destructive        
  end

Answer 1

您可以修补Matrix类以删除列...

class Matrix
  def drop_column
    @rows.each {|r| r.pop}
  end
end


my_matrix = Matrix.build(3,5) { 1 }
=> Matrix[[1, 1, 1, 1, 1], [1, 1, 1, 1, 1], [1, 1, 1, 1, 1]] 

my_matrix.drop_column

p my_matrix
 => Matrix[[1, 1, 1, 1], [1, 1, 1, 1], [1, 1, 1, 1]]

或类似地删除一行

class Matrix
  def drop_row
    @rows.pop
  end
end

修改

所以实际上hpop会......

def hpop(number_of_columns = 1)        
  Matrix.Raise ErrDimensionMismatch unless number_of_columns < column_count

  dropped_columns = []
  number_of_columns.times do
    dropped_column = []      
    @rows.each {|r| dropped_column << r.pop}
    dropped_columns << dropped_column
  end

  @column_count -= number_of_columns

  Matrix.columns(dropped_columns.reverse)
end

（代码来自您自己的来源，只是添加了@column_count -= ...行）

编辑＃2

vpop方法可能会......

class Matrix
  def vpop(number_of_rows = 1)
    Matrix.Raise ErrDimensionMismatch unless number_of_rows < @rows.size
    dropped_rows = []
    number_of_rows.times { dropped_rows.unshift @rows.pop }
    Matrix.columns(dropped_rows)
  end
end

替换Matrix对象的内部状态

1 个答案: