功能: 统计矩阵里每个元素出现的次数

格式: DataCountByValue(a)

a: 为待统计的矩阵变量

说明: 
1、本函数返回2列的矩阵变量, 第1列为a当中的元素值, 第2列为a当中元素置在a中出现的次数.
2、本函数返回的结果中,按出现次数由高到低的情况返回结果

例子:
a =
[ 6.00000000000000    7.50000000000000    1.50000000000000    13.5000000000000
  13.5000000000000    9.00000000000000    9.00000000000000    1.50000000000000
  1.50000000000000    15.0000000000000    3.00000000000000    1.50000000000000
  9.00000000000000    6.00000000000000    6.00000000000000    7.50000000000000 ]
b = DataCountByValue(a)//回车得到如下结果
b =
[ 1.50000000000000    4.00000000000000
  6.00000000000000    3.00000000000000
  9.00000000000000    3.00000000000000
  7.50000000000000    2.00000000000000
  13.5000000000000    2.00000000000000
  15.0000000000000    1.00000000000000
  3.00000000000000    1.00000000000000 ]