how to make a roc curve on matlab

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?

Answer 1

[Meg Noah]

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:

[Namarta Kapil]

Thanks for the reply. But now I am getting the following error: "Unable to open file 'prelim data for ROCs.xlsx' as a workbook. Check that the file exists, read

access is available, and the file is a valid spreadsheet file." I have imported the file multiple times now and I am still getting the error message

[Meg Noah]

it sounds like it is not in your path - is the file in your current working directory?

also - it shouldn't be confused by spaces in the filename, but it could be the operating system so you might want to rename the file

[Namarta Kapil]

I was able to generate the ROC curve. Thanks for your help.

[Meg Noah]

Great! If you're satisfied, do you mind accepting the answer?

[Namarta Kapil]

Hi,

I have been using this code in the computer in my lab and it works fine but for some reason on my personal computer its giving the following error:

"Error using readtable (line 223)

Unable to determine range. Range must be of the form 'A1' (cell), 'A:B' (column-select), '1:5' (row-select), 'A1:B5' (rectangle-select), or a valid named range in the sheet."

Would you be able to tell me what this means and how to remedy it?