What does this line of code do?

I've been given a classifier performance evaluation code I'm trying to understand and run. The first line of code gives an error on my data.

ACTUAL = 9957x1 Categorical (My class labels)

When the code reaches the first line

idx = (ACTUAL()==1);

it says Invalid types for comparison. What exactly is this line of code trying to do? Understanding this will help me fix it.

Here's the function code:

 function EVAL = Evaluate(ACTUAL,PREDICTED)
% This fucntion evaluates the performance of a classification model by 
% calculating the common performance measures: Accuracy, Sensitivity, 
% Specificity, Precision, Recall, F-Measure, G-mean.
% Input: ACTUAL = Column matrix with actual class labels of the training
%                 examples
%        PREDICTED = Column matrix with predicted class labels by the
%                    classification model
% Output: EVAL = Row matrix with all the performance measures


idx = (ACTUAL()==1);

p = length(ACTUAL(idx));
n = length(ACTUAL(~idx));
N = p+n;

tp = sum(ACTUAL(idx)==PREDICTED(idx));
tn = sum(ACTUAL(~idx)==PREDICTED(~idx));
fp = n-tn;
fn = p-tp;

tp_rate = tp/p;
tn_rate = tn/n;

accuracy = (tp+tn)/N;
sensitivity = tp_rate;
specificity = tn_rate;
precision = tp/(tp+fp);
recall = sensitivity;
f_measure = 2*((precision*recall)/(precision + recall));
gmean = sqrt(tp_rate*tn_rate);

EVAL = [accuracy sensitivity specificity precision recall f_measure gmean];

Answer 1

[Cris LaPierre]

You have a data type mismatch. You are passing in a variable (Actual) that is categorical, while the function you are using expects it to be either numeric or logical.

A=1:5

A = 1×5

1 2 3 4 5

idx1 = (A==1)

idx1 = 1×5 logical array
   1   0   0   0   0

% Now as categorical
B=categorical(1:5)

B = 1×5 categorical array
     1      2      3      4      5 

idx2 = B==1

Error using == (line 30)
Invalid types for comparison.

[Asim Shahzad]

So this function will only work with class labels that are numerical?

[Cris LaPierre]

I haven't tested your function, but the line of code giving the error will only work for numeric and logical data.