I'm trying to write a user-defined function which should determine whether there are any duplicate values in an array.

I'm trying to write a user-defined function. This function should determine if an array contains any values which occur more than once, and change the variable bmatch to 1 for true or 0 for false.

At the moment, I'm just trying to work out the algorithm of the function; the script will sometimes work and sometimes not, e.g., when I create an array [4 5 3 4 6 7 8] it won't detect the duplicate, but when the array is [4 5 3 4] it does detect the duplicate.

%data = [4 5 3 4 6 7 8];

for b = 1:length(data)

if sum(data(b) == data) > 1

bmatch = 1;

else

bmatch = 0;

end

end

Please let me know what I'm doing wrong, and if you have a solution to the issue.

[VBBV]

May be you need this change in your code

data = [4 5 3 4 6 7 8 10 2 10 2 20 21 7];
for b = 1:length(data)
    %  this change
    if sum(data(b)-data == 0) > 1
        % uncomment the below line to show if there is a duplicate value
        bmatch = 1;
        fprintf('bmatch = %d Num %d\n',bmatch,data(b))
    else
        bmatch = 0;
    end
end 

bmatch = 1 Num 4
bmatch = 1 Num 4
bmatch = 1 Num 7
bmatch = 1 Num 10
bmatch = 1 Num 2
bmatch = 1 Num 10
bmatch = 1 Num 2
bmatch = 1 Num 7

Answer 1

[Sai Kiran]

Hi,

As per my understanding you want a user defined function which returns 1 if any value in the array gets repeated or else 0.

Your code detects the duplicate values but the variable 'bmatch' will only gives the case for the last value in the array. Adding a 'break' keyword whenever you detect a duplicate value ensures you to go out of the loop and give the correct answer.

Here is the modified code for the same.

for b = 1:length(data)
    if sum(data(b) == data) > 1
        bmatch = 1;
        break;
    else
        bmatch = 0;
    end
end 

I hope it helps!

Thanks.

[Jonah]

Thanks for your reply Sai,

I managed to figure it out and I did indeed use the 'break' function. This is how I ended up writing the function if you care to know:

function bmatch = checkdata(data)

bmatch = 0;

for b = 1:length(data)

if sum(data(b)-data == 0) > 1

bmatch = 1;

break

end

end

end

[Stephen23]

Note that you do not need to loop over all elements, nor is it required to compare against all elements on every iteration. If speed is important then consider other approaches e.g.:

checkdata1([4,5,3,4,6,7,8])

ans = logical
   1

checkdata1([4,5,3,4])

ans = logical
   1

checkdata2([4,5,3,4])

ans = logical
   1

V = 1:1e5;
tic
checkdata0(V)

ans = logical
   0

toc

Elapsed time is 8.944594 seconds.

tic
checkdata1(V)

ans = logical
   0

toc

Elapsed time is 6.015339 seconds.

tic
checkdata2(V)

ans = logical
   0

toc

Elapsed time is 0.003918 seconds.

function bmatch = checkdata0(data) % your function
bmatch = false;
for b = 1:length(data)
    if sum(data(b)-data == 0) > 1
        bmatch = true;
        break
    end
end
end

function bmatch = checkdata1(data) % only check remaining elements
bmatch = false;
for k = 2:numel(data)
    if nnz(data(k-1)==data(k:end))
        bmatch = true;
        break
    end
end
end

function bmatch = checkdata2(data)
bmatch = ~all(diff(sort(data)));
end

[VBBV]

@Jonah @Sai Kiran, One problem with using break inside a loop, is it exits the loop once a duplicate value of a number is found in vector and doesn't check if there are more than one duplicate numbers present in vector.