How can I iterate over the keys and elements in a containers.Map?

D = containers.Map('air',1)

for k = keys(D)
    D(k)
end

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

Why does the above cause an error?

Answer 1

[KSSV]

D = containers.Map({'2R175', 'B7398', 'A479GY', 'NZ1452'}, ...
    {'James Enright', 'Carl Haynes', 'Sarah Latham', ...
     'Bradley Reid'});
 k = keys(D) ;
 val = values(D) ;
 for i = 1:length(D)
     [k{i} val{i}]
 end

[Diego Mancevo]

Thanks a lot!

[Steven Lord]

The code in the original question was very close. The reason it didn't work is because the keys in D are char vectors

>> D = containers.Map({'2R175', 'B7398', 'A479GY', 'NZ1452'}, ...
       {'James Enright', 'Carl Haynes', 'Sarah Latham', ...
        'Bradley Reid'})

D = 

Map with properties:

        Count: 4
      KeyType: char
    ValueType: char

The keys method returns a cell array, each cell of which contains one of the char vectors, not a char array itself. This allows containers.Map to return a set of char vector keys that are not the same length without needing to pad the shorter ones to the same length as the longest. To index into D, extract the char vectors from the cell array and use those char vectors as the index.

for k = keys(D)
  thekey = k{1}; % The curly braces are the key, so to speak
  fprintf('The value associated with key %s is %s.\n', ...
    thekey, D(thekey));
end

Answer 2

[Qixiang Zou]

D = containers.Map('air',1)
for k = keys(D)
    D(k{1}})
end

This should work. Iterator of cell returns element wrapped in a cell. So, add a stupid {1} can save your code.

Answer 3

[Clark Steen]

Alternatively, using strings:

D = containers.Map('air',1);
for k = string(D.keys)
    D(k)
end

ans = 1