Align different starting point to zero

I have a matrix , 7096*3 double.

At a first column, numbers represent same particles with different number. I have 168 particles and each of them has different starting time points(second column) with intensity value(third column). In the case of 40th particles, it starts from 2.1960 (see, the matrix, 40 from first column and 2.196 from second column).

I'd like to align those data to zero as the starting point. I need to find inital value or minimum value of time column of each particle and substract them. And make new matrix, probably. How can I do for that?

40 2.196 51950

40 3.294 51728

40 4.392 50899

40 5.490 50869

40 6.588 51741

-> What I want to do is

40 0 51950

40 1.098 51728

40 2.196 50899

40 3.294 50869

40 4.392 51741

number=unique(B(:,1));
tn=length(unique(B(:,1)));

for k=1:tn
   B(B(:,1)==number(k),2)-min(B(B(:,1)==number(k),2));
   
   
end
   

Answer 1

[Sayyed Ahmad]

try with find and index

for i=1:tn
    ind=find(B(:,1)==number(i))
    y=min(B(ind,2));
    B(ind,2)=b(ind,2)-y;
end

[Jaehwi Bong]

Thank you very much!