MATLAB: How to make a roc curve on matlab

roc curve

I want to generate a ROC curve for the data in the attached excel sheet. I am using the following code:
meanthresh = 0.8:0.1:2.5; % This alters the mean threshold between 0.8 and 2.5 by 0.1
%% Beginning the Mean ROC
for a = 1:length(meanthresh) %% the for loop makes it to where the threshold is automatically altered and you do not have to do it manually
positive_a = meanthresh(a) < (prelimdataforROCs(:, 3)); % declaring an algorithm to determine if the value is greater than the threshold
true = prelimdataforROCs(:, 1) == 1; %true = if the data in the column is equal to (==) 1
false = prelimdataforROCs(:, 1) == 0; %false = if the data in the column is equal to (==) 0
TP = sum(positive_a(true)); %true positive = if both the true statement (true) and the positive statement (positive_a) are met, then sum all the true values
FP = sum(positive_a(false)); %false positive = if both the false statement (false) and the positive statement (positive_a) are met, then sum all the false values
FN = sum(true) – TP; %false negative = sum of all true values minus the true positives
TN = sum(false) – FP; %true negative = sum of all false values minus the false positives
sensitivity_a(a) = (TP/(TP+FN)); %%sensitivity equation
specificity_a(a) = (TN/(TN+FP)); %%specificity equation
end %% end of for loop
stdevthresh = 0:0.1:1.7; %This alters the st dev threshold from 0 to 1.7 by 0.1
% Beginning of St Dev ROC
for b = 1:length(stdevthresh)
positive_b = stdevthresh(b) < (prelimdataforROCs(:, 4)); % declaring an algorithm to determine if the value is greater than the threshold
true = prelimdataforROCs(:, 1) == 1; %true = if the data in the column is equal to (==) 1
false = prelimdataforROCs(:, 1) == 0; %false = if the data in the column is equal to (==) 0
TPsd = sum(positive_b(true)); %true positive = if both the true statement (true) and the positive statement (positive_b) are met, then sum all the true values
FPsd = sum(positive_b(false)); %false positive = if both the false statement (false) and the positive statement (positive_b) are met, then sum all the false values
FNsd = sum(true) – TPsd; %false negative = sum of all true values minus the true positives
TNsd = sum(false) – FPsd; %true negative = sum of all false values minus the false positives
sensitivity_b(b) = (TPsd/(TPsd+FNsd)); %%equations for sensitivity and specificity
specificity_b(b) = (TNsd/(TNsd+FPsd));
end
plot(1-specificity_b, sensitivity_b, 'Marker', '.', 'MarkerSize', 16, 'LineWidth', 1); %%this is the standard deviation plot
hold on %%allows more than one graph to be on the same plot–must be followed by "hold off" when done
plot(1-specificity_a, sensitivity_a, 'Marker', '.', 'MarkerSize', 24, 'LineWidth', 1); %%plotting command for the mean ROC
hold off
legend('St. Devs', 'Averages'); %%this puts a legend on the graph–legend('first name', 'second name')
xlabel('False Positive Rate'); %%label on x axis
ylabel('True Positive Rate'); %%label on y axistitle('ROC for Mean Path Length'); %%title of graph
But I am getting the following error: "Undefined operator '<' for input arguments of type 'table'."
Can you please tell me where I am going wrong?

Best Answer

I was able to run a slightly modified version with no errors. I do not know if it is doing what you want it to do.
% I want to generate a ROC curve for the data in the attached excel sheet. I am using the following code:
meanthresh = 0.8:0.1:2.5;  % This alters the mean threshold between 0.8 and 2.5 by 0.1
rocTable = readtable('prelim data for ROCs.xlsx','range','$A3:$D18');
%% Beginning the Mean ROC
for a = 1:length(meanthresh)  %% the for loop makes it to where the threshold is automatically altered and you do not have to do it manually
    
    positive_a = meanthresh(a) < (rocTable.Average);  % declaring an algorithm to determine if the value is greater than the threshold

    true = rocTable.FID == 1; %true = if the data in the column is equal to (==) 1

    false = rocTable.FID == 0; %false = if the data in the column is equal to (==) 0

    TP = sum(positive_a(true));  %true positive = if both the true statement (true) and the positive statement (positive_a) are met, then sum all the true values
    FP = sum(positive_a(false));  %false positive = if both the false statement (false) and the positive statement (positive_a) are met, then sum all the false values
    FN = sum(true) - TP; %false negative = sum of all true values minus the true positives

    TN = sum(false) - FP; %true negative = sum of all false values minus the false positives 

    
    sensitivity_a(a) = (TP/(TP+FN)); %%sensitivity equation
    specificity_a(a) = (TN/(TN+FP)); %%specificity equation
    
end  %% end of for loop
 
stdevthresh = 0:0.1:1.7; %This alters the st dev threshold from 0 to 1.7 by 0.1
 
% Beginning of St Dev ROC
for b = 1:length(stdevthresh)
    
positive_b = stdevthresh(b) < (rocTable.SD);  % declaring an algorithm to determine if the value is greater than the threshold
    true = rocTable.FID == 1; %true = if the data in the column is equal to (==) 1
    false = rocTable.FID == 0; %false = if the data in the column is equal to (==) 0
    TPsd = sum(positive_b(true)); %true positive = if both the true statement (true) and the positive statement (positive_b) are met, then sum all the true values 
    FPsd = sum(positive_b(false)); %false positive = if both the false statement (false) and the positive statement (positive_b) are met, then sum all the false values
    FNsd = sum(true) - TPsd; %false negative = sum of all true values minus the true positives
    TNsd = sum(false) - FPsd; %true negative = sum of all false values minus the false positives 
    
    sensitivity_b(b) = (TPsd/(TPsd+FNsd)); %%equations for sensitivity and specificity
    specificity_b(b) = (TNsd/(TNsd+FPsd));
    
end
 
plot(1-specificity_b, sensitivity_b, 'Marker', '.', 'MarkerSize', 16, 'LineWidth', 1); %%this is the standard deviation plot
hold on  %%allows more than one graph to be on the same plot--must be followed by "hold off" when done
plot(1-specificity_a, sensitivity_a, 'Marker', '.', 'MarkerSize', 24, 'LineWidth', 1);  %%plotting command for the mean ROC
hold off
legend('St. Devs', 'Averages');  %%this puts a legend on the graph--legend('first name', 'second name')
xlabel('False Positive Rate');   %%label on x axis
ylabel('True Positive Rate'); %%label on y axistitle('ROC for Mean Path Length'); %%title of graph
% But I am getting the following error: "Undefined operator '<' for input arguments of type 'table'." 
% Can you please tell me where I am going wrong?
The resulting image is:
roc.png
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