Asked by Anil Kamath
on 16 Nov 2018

I have discovered that the following code worked in Matlab 2018a but now throws an error in 2018b:

mode(["A","A","B"],2)

It would appear that the new version of matlab only allows computing the mode on numeric arrays. Is this a bug, or a known change to how this function works (I know that in this version, some of these functions now operate on multiple dimensions now)? And is there a quick workaround? So far I've created the following hack to operate on strings, though I expect it's pretty inefficient:

Y = strings(1,size(X,2));

for n = 1:size(Y,2)

C = categorical(X(:,n));

CC = categories(C);

[~,ind] = max(countcats(C));

if ~isempty(ind)

Y(n)=string(CC(ind));

end

end

Answer by Adam Danz
on 16 Nov 2018

Edited by Adam Danz
on 16 Nov 2018

Accepted Answer

The documentation for both 2018a and 2018b indicate that the first input to mode() "can be a numeric array, categorical array, datetime array, or duration array." One workaround would be to change your string to a categorical vector.

This works in 2018b

mode(categorical( ["A","A","B"]))

ans =

categorical

A

If needed, you could convert back to a string:

string(mode(categorical( ["A","A","B"])))

Anil Kamath
on 19 Nov 2018

Thanks!

It's a shame this doesn't work using the native mode function on strings, as it means you can't quickly compute the mode in a 2D array along a single dimension without converting each slice into a categorical array one by one, and computing the mode of each categorical slice. It feels like a very natural interpretation for the mode of a string to be the string which occurs most frequently...

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Answer by Philip Borghesani
on 16 Nov 2018

Use a character vector instead of a string array:

mode(['A','A','B'],2)

% or

mode('AABBCCC',2)

I belive it was a bug that it worked with strings in R2018a. It has always worked with character vectors and sombody was a bit too helpful adding support for strings which can’t simply be treated as a numeric value.

Anil Kamath
on 19 Nov 2018

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