code: def matrixValues(matrix,key):
      
      assert key in matrix.dtype.names
      col=matrix.dtype.names.index(key)
      values=np.empty(len(matrix))*np.nan
      for i in range(len(matrix)):
          values[i]=matrix[i][col]
      return values
docs: given a key, return a list of values from the matrix with that key.