STL map--> sort by value?

Question

Hi

I wonder how can I implement the STL map sorting by value.

For example, I have a map m

map<int, int>;
m[1] = 10;
m[2] = 5;
m[4] = 6;
m[6] = 1;

and then.. I'd like to sort that with the m's value. So, if I print the map, I'd like to get the result like

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

this.

How can I sort like this way? Is there any way that I can deal with the key and value with sorted values?

Answer 1

I wonder how can I implement the STL map sorting by value.

You can’t, by definition. A map is a data structure that sorts its element by key.

Answer 2

You should use Boost.Bimap for this sort of thing.

Answer 3

You can build a second map, with the first map's values as keys and the first map's keys as values.

Answer 4

Dump out all the key-value pairs into a set<pair<K, V> > first, where the set is constructed with a less-than functor that compares the pair's second value only. That way, your code still works even if your values aren't all distinct.

Or dump the key-value pairs into a vector<pair<K, V> >, then sort that vector with the same less-than functor afterwards.