怎么合并矩阵

问题：已知矩阵aa和bb，怎么可以得到cc？ 也即是怎么按照矩阵的行名字将两个或多个矩阵进行合并。谢谢

aa=matrix(c(1,2,3),nrow=3,ncol=1)
rownames(aa)=c("x1","x2","x5")
aa

bb=matrix(c(11,12,17,5),nrow=4,ncol=1)
rownames(bb)=c("x1","x3","x4","x5")
bb

cc=matrix(c(1,2,0,0,3,11,0,12,17,5),nrow=5,ncol=2)
rownames(cc)=c("x1","x2","x3","x4","x5")
cc


矩阵具体形式
> aa#####解释aa矩阵行名只有x1,x2,x5
   [,1]
x1    1
x2    2
x5    3
> bb解释bb矩阵行名只有x1,x3,x4,x5
   [,1]
x1   11
x3   12
x4   17
x5    5
> cc解释cc矩阵是将aa和bb矩阵合并，行名是x1:x5,第一列是aa矩阵元素（aa矩阵没有的赋值为0），第二列是bb矩阵元素
   [,1] [,2]
x1    1   11
x2    2    0
x3    0   12
x4    0   17
x5    3    5

1. aa=matrix(c(1,2,3),nrow=3,ncol=1)
   
2. rownames(aa)=c("x1","x2","x5")
   
3. aa
   
4. bb=matrix(c(11,12,17,5),nrow=4,ncol=1)
   
5. rownames(bb)=c("x1","x3","x4","x5")
   
6. #bb=data.table(bb)
   
7. bb
   
8. x=sort(union(rownames(aa),rownames(bb)))
   
9. a=setdiff(x,rownames(aa))
   
10. a1=which(x%in%a);a2=which(x%in%rownames(aa))
    
11. aa[a2]=aa;aa[a1]=0
    
12. aa
    
13. b=setdiff(x,rownames(bb))
    
14. b1=which(x%in%b);b2=which(x%in%rownames(bb))
    
15. bb[b2]=bb;bb[b1]=0
    
16. bb
    
17. cc=data.frame(aa,bb)
    
18. rownames(cc)=x
    
19. cc

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