Can I vectorize extraction of data from a cell array in MATLAB? - matlab

Question

I am wondering if it is possible to use a vector to access data within a cell array. I am hoping to accomplish this using a vectorized approach rather than a for-loop.
I'm attempting to run a simple microsimulation in MATLAB. I have a simulated cohort that is initially healthy, but some are at low risk for a particular disease while others are at high risk. Thus, I have an array (Starting_Cohort) that indicates each patient's risk level (first column) and their initial status (second column). In addition, I have a cell array (pstar) that indicates each patient's likelihood of transitioning between two hypothetical health states (i.e., "healthy" and "sick").
What I would like to accomplish is the following:
1) During each period of the simulation (t = 1:T), use the first column of the starting cohort to determine the patient's risk level (i.e., 1 or 2).
2) Use the risk level to access a specific row (dependent on their current health status) within a specific cell (dependent on their risk level) of the cell array.
3) Compare the resultant vector against a random draw from the uniform distribution (contained in the array "r"), and select the column number associated with the first value larger than that draw (the column number determines their health state in the subsequent period).
HOWEVER, I want to avoid doing this for one patient at a time (i.e., introducing a nested loop), as this increases the execution time of the code by an order of magnitude (the actual cohort consists of approximately 20000 patients). I've been trying to accomplish this through vectorization - that is, running the simulation over the entire patient cohort concurrently - but I hit a roadblock when trying to access data from the cell array described above.
Starting_Cohort = [1 1; 1 1; 2 1; 2 1;];
[Cohort_Size, ~] = size(Starting_Cohort);
pstar = cell(2, 1);
pstar{1, 1} = [0.75 1.00; 0.15 1.00]; pstar{2, 1} = [0.65 1.00; 0.25 1.00];
rng(1234, 'twister'); T = 5; r = rand(Cohort_Size, T);
Sim_Results = [Starting_Cohort zeros(Cohort_Size, T)];
for t = 1:T
[~, Sim_Results(:, t+2)] = max(pstar{Sim_Results(:, 1), 1} ...
(Sim_Results(:, t+1), :) > r(:, t), [], 2);
end
When I run the above code, I obtain the error "Expected one output from a curly brace or dot indexing expression, but there were 4 results." I take this to mean that my approach to extracting information from the cell array is inappropriate, although I'm not sure whether I can address this or how. I would be deeply appreciative for any assistance rendered!
UPDATE 070619: I did eventually get this to work, using the code below. Effectively, I created a string array containing the expression I wanted to apply to each row. The expression is identical for every row EXCEPT in that it contains the row index. I can then use arrayfun and evalin to produce results similar to those I was looking for. Unfortunately, my own problem involves sparse arrays, so I could not actually solve my original problem. However, I'm hoping this information may nonetheless be useful for others.
Starting_Cohort = [1 1; 1 1; 2 1; 2 1;];
[Cohort_Size, ~] = size(Starting_Cohort);
pstar = cell(2, 1);
pstar{1, 1} = [0.75 1.00; 0.15 1.00];
pstar{2, 1} = [0.65 1.00; 0.25 1.00];
rng(1234, 'twister'); T = 5; r = rand(Cohort_Size, T);
Sim_Results = [Starting_Cohort zeros(Cohort_Size, T)];
for i = 1:Cohort_Size
TEST(i, 1) = strcat("max(pstar{Sim_Results(", string(i), ", 1), 1}",...
"(Sim_Results(", string(i), ", t+1), :) > ", ...
"r(", string(i), ", t), [], 2)");
end
for t = 1:T
[~, Sim_Results(:, t+2)] = arrayfun(#(x) evalin('base', x), TEST);
end