[R] sorting a matrix by a different colnames order

[portnoy at supereva.it]

Hi R users,
I would like to know how to sort a matrix according a different order of 
colnames (or rownames) ,e.g.,
mx = matrix(rnorm(1:20),5,4)
colnames(mx) = letters[1:4]
rownames(mx) = letters[1:5]
mx
             a          b          c           d
a  0.02362598 -0.7033460  0.8106089 -1.03456219
b -0.45021522 -1.5769522  0.1770634  0.27997249
c  1.34732392  0.2956623  2.0027231 -0.85321627
d  0.82314457  1.2698347 -0.5468151  0.05806375
e -0.18668401 -0.4210383  0.6263465 -0.18889031

(new.col.names = sample(letters[1:4]))
[1] "a" "b" "d" "c"

so the new matrix has to be ordered according the new.col.names,i.e.,
             a          b           d          c
a  0.02362598 -0.7033460	-1.03456219  0.8106089
b -0.45021522 -1.5769522	 0.27997249  0.1770634
c  1.34732392  0.2956623	-0.85321627  2.0027231
d  0.82314457  1.2698347	 0.05806375 -0.5468151
e -0.18668401 -0.4210383	-0.18889031  0.6263465

Hope this is not a "basic question"

Thank you for your help.

Paolo