merge每行就是一步一步聚的过程，height是聚时的两类距离

我看到R对于merge的英文解释是        

an n-1 by 2 matrix. Row i of merge describes the merging of clusters at step i of the clustering. If an element j in the row is negative, then observation -j was merged at this stage. If j is positive then the merge was with the cluster formed at the (earlier) stage j of the algorithm. Thus negative entries in merge indicate agglomerations of singletons, and positive entries indicate agglomerations of non-singletons.

像下面的结果 第一行-7，-8分别是什么意思啊 还有如果遇到负数行或者正数行聚类是怎么进行的？

> cbind(res1$merge,res1$height)
      [,1] [,2]      [,3]
[1,]   -7   -8  105.1565
[2,]   -4   -5  138.1701
[3,]  -28  -30  189.6000
[4,]   -3    1  194.3796
[5,]  -15  -31  196.4032
[6,]  -10  -23  234.9086
[7,]   -6  -29  235.2408
[8,]  -27    3  244.4392

第一行 将第七个观测点和第八个观测点聚为一类
第二行 将第四和第五聚为一类
...
第四行 将第3个观测点聚到第一行聚的那一类

喔 原来是这样的啊 非常感谢