subletting an array according to dimnames

Hi all,
  I have a three dimensional array with the corresponding dimension names.
I would like to subset the array according to the dimension names. For
example,
suppose I want to extract the values corresponding to A=20, B=10, C=0.  I
know I
can do:
 P2[dimnames(P2)$A==20, dimnames(P2)$B==10, dimnames(P2)$C==0]

But is there a better way for doing this? Thanks for your help!
  Hanna

dimnames(P2)

$A

[1] "20" "25" "30" "35" "40"


$B

[1] "5"  "10" "15" "20" "25" "30" "35" "40"


$C

[1] "0"  "5" "10" "15" "20" "25" "30" "35"