MATLAB how to use FIND function with IF statement

Programmer Question

This question is related to http://stackoverflow.com/questions/3071558/matlab-how-to-merge-data

how to use the FIND function with IF statement? e.g. if I have this data:

20  10  1
20  11  1
20  15  1
23  10  1
23  10  1
23  12  0

Rule 1:
Data of column 3 must be 1.

Rule 2:
If n is the current index of column 1, if n equal n-1 (20=20) of column 1, data of column 2 of index n and n-1 is merged.

20  21  0
20  15  0
20  0   0
23  20  0
23  0   0
23  12  0

fid=fopen('data.txt');
A=textscan(fid,'%f%f%f');    
code=A{1};
time=A{2};
mark=A{3};
fclose(fid);

Find the answer here