For loop over written output

Hello,

I seem to keep running into this problem again and again. So I would really appreciate if someone could explain what I should do here?

Every time the outer for loop (i=1:s_m) runs, it overwrites the results from the previous nested for loop run (k=1:s). How can I solve this so that the results go in the subsequent column regardless of how many times I run the outer loop?

For the final answer, I want an array (Z) with 3 cols, and as many number of rows as needed (depending on user input). Currently Z has 500 rows because I initialized to an arbritaty overly conservative number.

Please help! I am really new to MATLAB (2018b). I don't just want an answer to this specific problem. I would really like to understand how to get for loops to not overwrite solutions in general.

matches=cell array; reactionType=string array

matches=L(idx);
s_m=length(matches);
Z=cell(500,3); 
for i=1:s_m
    s=length(matches{1,i});
    for k=1:s
        q(k)=matches{1,i}(k,1);
        Z(k,1)={q(k)};
        Z(k,2)={reactionType(q(k),3)};
        Z(k,3)={reactionType(q(k),2)};  
    end
end

Answer 1

[Walter Roberson]

matches = L(idx);
s_m = length(matches);
num_matches = arrayfun(@length, matches);
Nz = sum(num_matches);
Z = cell(Nz,3);
r = 0;
for i = 1:s_m
    s = num_matches(i)
    for k = 1:s
        q = matches{1,i}(k,1);
        r = r + 1;
        Z{r, 1} = q;
        Z{r, 2} = reactionType(q,3);
        Z{r, 3} = reactionType(q,2);  
    end
end

[Ishita Trivedi]

what does @arrayfun(...) do?