Feng,
Hello, all of this behavior comes down to argument recycling.
Feng Li wrote:
Dear R,
I have two small questions confused me recently. Now assume I have a matrix
"a", like this,
a <- matrix(1:6, 2, 3)
a
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
I sometimes need each row of "a" raised to a different exponent. So I do a
trick like this,
a^c(2, 3)
[,1] [,2] [,3]
[1,] 1 9 25
[2,] 8 64 216
Right, so you have
as.vector(a)
[1] 1 2 3 4 5 6
and
a^c(2,3)
will then use argument recycling to compute
1^2 2^3 3^2 4^3 5^2 6^3
and then return the matrix in its original dimension.
My first question is that if it is possible to do this trick column wise?
Yes, just use t to transpose.
Just out of curiosity, of course I know there are other ways of doing this.
And the second question is why I get such result when I put another element
in the exponent part like this,
a^c(2, 3, 4)
[,1] [,2] [,3]
[1,] 1 81 125
[2,] 8 16 1296
Same reason as it worked above, argument recycling, now you get
1^2 2^3 3^4 4^2 5^3 6^4
BTW, I have a 64bit R version (2.11) for Linux. Any advice would be
appreciated.
Feng
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