Can anyone please explain me this line of a code?

probability = arrayfun(@(x) mean(audR(audR(:,1)==x,2)==2) , contrast);

[Adam]

array fun runs the specified function on each element of the input array in turn, as described in

doc arrayfun.

Mean is a simple function described in

doc mean

Here it is used as part of an anonymous function:

@(x) mean( audR(audR(:,1)==x,2)==2)

which can be taken out and run on command line to see what it does to an individual input if you assign that to a variable e.g.

f = @(x) mean( audR(audR(:,1)==x,2)==2)
f( 7 )

[jasmine]

Thank you for your answer. But what I don't actually understand is this part:

(audR(audR(:,1)==x,2)==2)

[Adam Danz]

audR is not a built-in function in matlab. If you search for that term on this forum, your post is the only post that contains this term. Searching for it on Google also didn't reveal anything. So it's a custom function not available to us.

If you execute this line below you can find the file and open the hood to see what it does.

which('audR','-all')

If that doesn't find the file, it might be an annonymous function local to the file from which you took that line of code. Or perhaps it's a function that you don't have at all.

[Adam Danz]

Ahhh... yeah it's an array (blush).

@Iuliana,

audR(:,1)==x %this produces a logical index marking rows of the first 
             %column of audR that match the input value 'x'

audR(audR(:,1)==x,2) % for each of those rows from the comment above,
                     % you're extracting the data from the second 
                     % column of audR.  

(audR(audR(:,1)==x,2)==2) %and finally, you're determining whether those
                          % values are equal to 2.

Here's an example you can execute line by line to see what's going

% Produce fake data
audR = [[1;1;2;2;3;3],[1;2;1;2;1;2]]; 
x = 2 

audR(:,1)==x                    
audR(audR(:,1)==x,2) 
(audR(audR(:,1)==x,2)==2) 

[jasmine]

Thank you very much for your answer!

Answer 1

[Stephen23]

If audR is a matrix, then

audR(audR(:,1)==x,2)==2
%    ^^^^^^^^^           % first column of audR
%             ^^^        % ... is equal to x.
%    ^^^^^^^^^^^^        % used as a logical index into the rows of audR
%                 ^      % second column of audR
%                   ^^^  % ... is equal to 2.

So the code takes the rows of audR where the first column equals x, and checks if their second column equals 2.

[Adam Danz]

+1 for simple and effective explanation