storing values in for loop

I am currently working on a regression project using a subsampling method and am finding R^2 values for a particular data set. However, when I try to calculate the mean and the standard deviation for all the R62 values produed (over 1000 iterations) I get values from using only the last value. i.e std = o and mean = R^2 value from the 1000th iteration. As it stands my code is as below. Any help would be gretly appreciated.

B=1000;

for i = 1:B

N=size(gas_data,1);

idx = randperm(N);

idx_train = idx(1:floor(0.8*N)); % 0.8 => 80% of data for training

idx_test = idx(ceil(0.8*N):end);

gas_train_proxyCO = gas_data.PT08_S1_CO_(idx_train);

gas_test_proxyCO = gas_data.PT08_S1_CO_(idx_test);

gas_train_CO = gas_data.CO_GT_(idx_train);

gas_test_CO = gas_data.CO_GT_(idx_test);

x_diff = gas_test_proxyCO - mean(gas_test_proxyCO);

x_diff2 = x_diff .* x_diff;

Sxx = sum(x_diff2);

y_diff = gas_test_CO - mean(gas_test_CO);

y_diff2 = y_diff .* y_diff;

Syy = sum(y_diff2);

Sxy = sum(x_diff .* y_diff);

% now for correlation

r = Sxy / sqrt(Sxx*Syy);

% Compute beta's (b's)

b1 = Sxy / Sxx;

b0 = mean(gas_test_CO) - b1 * mean(gas_test_proxyCO);

% Predict:

gas_test_CO_hat = b0 + b1 * gas_test_proxyCO;

% Residuals

e = gas_test_CO - gas_test_CO_hat;

%Find Coefficiant of Determination

e2 = e.*e;

sse = sum(e2);

v = gas_test_CO - mean(gas_test_CO);

v2 = v.*v;

sst = sum(v2);

R2 = 1-(sse/sst)

a=std(R2)

b= mean(R2)

end

Answer 1

[Tyler F]

You arent storing the value for each loop. Every time it loops the values for a and b overwrite. I cant run your code without your data but modifying the last lines to be:

a(i)=std(R2)
b(i)= mean(R2)

would put them into a vector.