How can I sort a Map by values ?

For the example below, how can I sort the mapObj by values and of course the keys must also folow the valeus new order.

keySet = {'Jan', 'Feb', 'Mar', 'Apr'};

valueSet = [327.2, 368.2, 197.6, 178.4];

mapObj = containers.Map(keySet,valueSet);

[Adam]

containers.Map is an unsorted data structure. You can sort the values and keys if you extract them, but you cannot sort the map itself, it will always return the keys and values ordered alphanumerically by key.

[KL]

Thanks for the comment Adam, I removed my answer.

[sendja450]

thanks for your comments, if I want to extract theme I will lose the (key, value) property. So how can I extract in a for loop the max in each iteration in order to have a descending order ?

[Adam]

You can extract the keys and the values and do a sort on the keys, making sure to retain the 2nd output argument from sort - these are the indices required to apply to the values in order for them to be ordered to match the keys still e.g.

keys = myMap.keys;
values = myMap.values;

[sortedKeys, sortIdx] = sort( keys );
sortedValues = values( sortIdx );

[sendja450]

Thanks for your help @Adam.

Answer 1

[KUNHUAN]

IDEA

One way is to retrieve keys and values and sort them independently.

First, sort values. Then, sort keys. Lastly, reassign keys and values.

Using flip to sort in reverse order.

IMPLEMENTATION

keySet = {'Jan', 'Feb', 'Mar', 'Apr'};
valueSet = [327.2, 368.2, 197.6, 178.4];
mapObj = containers.Map(keySet,valueSet);

[mapObj, keys_map, values_map] = sort_map(mapObj) % Default: order="values", reverse=0

mapObj = 
  Map with properties:

        Count: 4
      KeyType: char
    ValueType: double

keys_map = 1×4 cell array
    {'Apr'}    {'Mar'}    {'Jan'}    {'Feb'}

values_map = 1×4

178.4000 197.6000 327.2000 368.2000

[mapObj, keys_map, values_map] = sort_map(mapObj, order="keys", reverse=1)

mapObj = 
  Map with properties:

        Count: 4
      KeyType: char
    ValueType: double

keys_map = 1×4 cell array
    {'Mar'}    {'Jan'}    {'Feb'}    {'Apr'}

values_map = 1×4

197.6000 327.2000 368.2000 178.4000

Define the following sort_map function.

function [output, keys_map, values_map] = sort_map (input, options)

    arguments
        input containers.Map; 
        options.order char = "values"; 
        options.reverse logical = 0; 
    end
    k = keys(input); 
    v = cell2mat(values(input)); 
    
    % Default return
    output = input; 
    keys_map = k; 
    values_map = v; 
    
    if (options.order == "keys")
        [k_new, order] = sort(k); 
        if (options.reverse == 1)
            k_new = flip(k_new); 
            order = flip(order); 
        end
        v_new = v(order); 
        output = containers.Map(k_new, v_new); 
        keys_map = k_new; 
        values_map = v_new; 
    elseif (options.order == "values")
        [v_new, order] = sort(v); 
        if (options.reverse == 1)
            v_new = flip(v_new); 
            order = flip(order); 
        end
        k_new = k(order); 
        output = containers.Map(k_new, v_new); 
        keys_map = k_new; 
        values_map = v_new; 
    end
    
end

REFERENCES

https://ww2.mathworks.cn/help/matlab/ref/sort.html

There is a section that introduces sorting with the same order:

%  X = [3 6 4 2 1 5];
%  Y = ["yellow" "purple" "green" "orange" "red" "blue"];
%  [Xsorted,I] = sort(X)
%  Ysorted = Y(I)

[Stephen23]

"Lastly, reassign keys and values" does nothing.

As Adam explained six years ago here, containers.Map is an unsorted data type, so this code makes absolutely no difference to the order of the keys and values of the containers.Map objects themselves:

keySet = {'Jan', 'Feb', 'Mar', 'Apr'};
valueSet = [327.2, 368.2, 197.6, 178.4];
mapObj0 = containers.Map(keySet,valueSet);
mapObj0.keys

ans = 1×4 cell array
    {'Apr'}    {'Feb'}    {'Jan'}    {'Mar'}

mapObj0.values

ans = 1×4 cell array
    {[178.4000]}    {[368.2000]}    {[327.2000]}    {[197.6000]}

mapObj1 = sort_map(mapObj0); % Default: order="values", reverse=0
mapObj1.keys

ans = 1×4 cell array
    {'Apr'}    {'Feb'}    {'Jan'}    {'Mar'}

mapObj1.values

ans = 1×4 cell array
    {[178.4000]}    {[368.2000]}    {[327.2000]}    {[197.6000]}

mapObj2 = sort_map(mapObj0, order="keys", reverse=1);
mapObj2.keys

ans = 1×4 cell array
    {'Apr'}    {'Feb'}    {'Jan'}    {'Mar'}

mapObj2.values

ans = 1×4 cell array
    {[178.4000]}    {[368.2000]}    {[327.2000]}    {[197.6000]}

function [output, keys_map, values_map] = sort_map (input, options)

arguments
    input containers.Map; 
    options.order char = "values"; 
    options.reverse logical = 0; 
end
k = keys(input); 
v = cell2mat(values(input)); 

% Default return
output = input; 
keys_map = k; 
values_map = v; 

if (options.order == "keys")
    [k_new, order] = sort(k); 
    if (options.reverse == 1)
        k_new = flip(k_new); 
        order = flip(order); 
    end
    v_new = v(order); 
    output = containers.Map(k_new, v_new); 
    keys_map = k_new; 
    values_map = v_new; 
elseif (options.order == "values")
    [v_new, order] = sort(v); 
    if (options.reverse == 1)
        v_new = flip(v_new); 
        order = flip(order); 
    end
    k_new = k(order); 
    output = containers.Map(k_new, v_new); 
    keys_map = k_new; 
    values_map = v_new; 
end

end