Hi all,

I have a data of 625 individual in a square grid of 25 by 25 located at the coordinates (1,1), (1, 2), ......, (1, 25),(2,1), (2,2),........, (2,25), ...........,(25, 1).................., (25,25) and they are infected at different times from 1 day to 10 days. Only one individual is infected at the first day, some are infected second day, some are third day and so on. Some individuals are non-infected so they are associated at day 0. Now I want  first to sort them out in the group of same infected day and want to sample randomly 10% of them from each group which are infected. 

Any idea and suggestion will be great for me.

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Ok lets make the things easier. I have data in the form:

X     Y    INFTIME
1     1     0
1     2     4
1     3     4
1     4     3
2     1     3
2     2     1
2     3     3
2     4     4
3     1     2
3     2     2
3     3     0
3     4     2
4     1     4
4     2     3
4     3     3
4     4     0

X and Y represent he X and Y components in the square grid of 4 by 4. Now I need and algorithm to short the matrix depending in the INFTIME. That is I want to make the group of the individuals of the same INFTIME, then I need to sample 10% from each group. I think this helps better to understand the problem.

[object XMLDocument]
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Ok here I want to make the thinks easier. In first step let I have a data in this matrix form
X