Calculate a return (base index)

I would like to calculate the column Base Index , for each particular ID is id(i)/id(base)*100, where id(base) is the first item FOR EACH id

ID  Value   Base Index
1  10  100
1  15  150 (e.g.15/10*100)
1  4  40   
2  3  100
2  20  667
2  8  267
2  11  367
3  25  100

with this code I only get right answers for first id...how can I deal with the last one?

bvalue(1)=100;
for i=2:length(id)-1
if id(i)~=id(i-1) & id(i)==id(i+1)
bvalue(i)=100;
else
bvalue(i)=value(i)/value(id(i))*100;
end
end

Answer 1

[the cyclist]

There were a couple small errors. I think I fixed them.

id = [1 1 1 2 2 2 2 3];
value = [10 15 4 3 20 8 11 25];

base = value(1);
bvalue(1)=100;
for i=2:length(id)
  if id(i)~=id(i-1)
    bvalue(i)=100;
    base = value(i);
  else
    bvalue(i)=value(i)/base*100;
  end
end

[Aleksandar]

thanks a lot!!