R help - Mar 2014 - heatmap indexing x axis and y axis

Dear all ,

I plotted a heat map of 20*20 matrix (lets say x axis and y axis comprises
of alphabets A,D.G.... and so on) which contain multiple values for each
entry in the dataset. I need to rearrange x axis and y axis on the basis of
similar properties on x axis and y axis such as A E,H  and appears at first
of a axis and y axis and subsequently then C,G,D on both axis.

 sample dataset

        D A 0.150
 D H 0.000
D E 1.000
 D E 0.820
D E 1.000
 G A 1.000
G E 0.520
 A G 0.190
A E 1.000
 A C 0.080
A C 0.200
 E D 0.120
E D      0.400
 H A 0.359
C G 0.214
 C D 0.421

 Many thanks

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