Calculating displacement many times with respect to different elements

I have the following data (or similar):

154240           1           7
154240           2           2
154240           5           6
154240           2           5
154240           6           7
154240           2           7
154240           5           6
154240           6           7
154240           4           6
154240           4           6
154240           4           6

641224           2           3
641224           2           1
641224           2           3
641224           1           2

641311           5           5
641311           7           5
It represents data of the form [tag number of rat, x coord, y coord] (as im studying a rat population). I would like to calculate the displacement of x & y with respect to the first x & y entries for each of the same value of the tag, i.e. I want an nx3 matrix (where n is size of my data) which gives me [tag number again,(0,x2-x1,x3-x1,x4-x1 etc),(0,y2-y1,y3-y1,y4-y1 etc)] but I am totally inept at programming and am flummoxed right now.

Any help is greatly appreciated!

[Sean de Wolski]

So what output do you expect for you above input? Please describe to us how you get that. Results are worth a 1000 words!

Answer 1

[Azzi Abdelmalek]

X your array

out=bsxfun(@minus,X,[0 X(1,2) X(1,3)])

[Timothy Russell]

This is great, but I the first x & y displacement for each different tag number needs to be (0,0) (as the displacement for the first time a rat is captured is (0,0)), and this isn't doing that. Is there an easy way to split up a matrix into seperate matricies by using the element in the first column (i.e. the tag number in this case)? Thanks though, it does what I wanted, I just haven't sort my data out properly yet!