How can I sort an STL map by value?

Question

How can I implement STL map sorting by value?

For example, I have a map m:

map m;
m[1] = 10;
m[2] = 5;
m[4] = 6;
m[6] =          


        

Answer 1

Create another map, provide a less() function based on the value not key, AND the function should return true if the value1 <= value2 (not strictly < ). In this case, elements with non-distinct values can be sorted as well.