storing values in for loop

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Ben Hatrick
Ben Hatrick 2022-1-4
编辑： Tyler F 2022-1-4
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

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回答（1 个）

Tyler F
Tyler F 2022-1-4
编辑：Tyler F 2022-1-4
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.

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