Rで行列の行と列に名前をつける

> x<-matrix(1:9,nrow=3,ncol=3)
> x
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8
[3,]    3    6    9
> str(x)
 int [1:3, 1:3] 1 2 3 4 5 6 7 8 9



> keys <- c("English","Math","Science")
> str(keys)
 chr [1:3] "English" "Math" "Science"

> colnames(x) <- keys
> str(x)
 int [1:3, 1:3] 1 2 3 4 5 6 7 8 9
 - attr(*, "dimnames")=List of 2
  ..$ : NULL
  ..$ : chr [1:3] "English" "Math" "Science"

> keys2 <- c("a","b","c")
> rownames(x) <-keys2
> x
  English Math Science
a       1    4       7
b       2    5       8
c       3    6       9
> str(x)
 int [1:3, 1:3] 1 2 3 4 5 6 7 8 9
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:3] "a" "b" "c"
  ..$ : chr [1:3] "English" "Math" "Science"

> x[1]
[1] 1

> x[[1]]
[1] 1

> x[,1]
a b c
1 2 3

> x["a"]
[1] NA

> x[1,"English"]
[1] 1

> x[,"English"]
a b c
1 2 3

# names()だと各要素に名前をつける
> names(x) <- keys
> x
  English Math Science
a       1    4       7
b       2    5       8
c       3    6       9
attr(,"names")
[1] "English" "Math"    "Science" NA        NA        NA        NA      
[8] NA        NA      
> str(x)
 int [1:3, 1:3] 1 2 3 4 5 6 7 8 9
 - attr(*, "dimnames")=List of 2
  ..$ : chr [1:3] "a" "b" "c"
  ..$ : chr [1:3] "English" "Math" "Science"
 - attr(*, "names")= chr [1:9] "English" "Math" "Science" NA ...

http://cse.naro.affrc.go.jp/takezawa/r-tips/r/26.html