从矩阵中提取特定值

Question

I have a symmetric matrix of form

 A  B  C  D  E

A 0 0 0 0 3

B 0 0 0 9 0

C 0 0 0 0 3

D 0 9 0 0 0

E 3 0 3 0 0

I need get some specific pair values from this (eg. BC, CD, E,D). Does someone know a function of "R" associated with a data frame that point out the names of row*colums? I need an "automatized" method because I'm trying with big matrices. Thank you Gastón

Answer 1

If you put data in dataframe, you can easily access all elements:

> ddf
  A B C D E
A 0 0 0 0 3
B 0 0 0 9 0
C 0 0 0 0 3
D 0 9 0 0 0
E 3 0 3 0 0
> 
> 
> ddf[1,1]
[1] 0
> ddf["A","B"]
[1] 0
> 
> ddf["E","B"]
[1] 0
> ddf["E","A"]
[1] 3
>