Not able to append to an empty container map

I've been trying to write a function that divides a matrix based on its 'class value' . For example, if we have an matrix like -

1	2	1
3	4	0
1	3	1
6	7	2
6	7	0
6	7	1

we should get

(class 1)
1 2 1
1 3 1
6 7 1 
and
(class 0)
3 4 0
6 7 0
and
(class 2)
6 7 2

I've written this so far using a container map, since I want to closely represent a Python dictionary.

I want to create a new key-value pair in the map if the class in focus is not already a key of the map. And if it already exists as a key, I want to append it to the existing value (which is a matrix) for that key.

function [separated] = separateByClass(dataset)
    % assume the class variable is the last column of the dataset
    % We return a container map mapping the unique class variables to the
    % row instances from the dataset
    
    separated = containers.Map;
    
    for i=1:size(dataset, 1)
        vector = dataset(i, :);
        class_var = vector(end);
        if isKey(separated, class_var)== 0
            separated(class_var) = vector;
        else
            separated(class_var) = [separated(class_var); vector];
        end
    end
    
end

Using the same matrix used as an example as the input 'dataset', I get an error on the first iteration of the for loop, on trying to run the line

separated(class_var) = vector;

The error I get is

Error using containers.Map/subsasgn
Specified key type does not match the type expected for this container.

Error in separateByClass (line 12)
            separated(class_var) = vector;

I can't figure how to fix the data type issue in this!

Answer 1

[Walter Roberson]

https://www.mathworks.com/help/matlab/ref/containers.map.html

The default key type is char, so use the keytype valuetype options to change the default.

[Sanjan Das]

Yes, changed the type to 'any', and works now! Thanks.