C++ Help finding the max value in a map
You can use std::max_element
to find the highest map value (the following code requires C++11):
std::map<int, size_t> frequencyCount;
using pair_type = decltype(frequencyCount)::value_type;
for (auto i : v)
frequencyCount[i]++;
auto pr = std::max_element
(
std::begin(frequencyCount), std::end(frequencyCount),
[] (const pair_type & p1, const pair_type & p2) {
return p1.second < p2.second;
}
);
std::cout << "A mode of the vector: " << pr->first << '\n';
You never changed currentMax
in your code.
map<int,unsigned> frequencyCount;
for(size_t i = 0; i < v.size(); ++i)
frequencyCount[v[i]]++;
unsigned currentMax = 0;
unsigned arg_max = 0;
for(auto it = frequencyCount.cbegin(); it != frequencyCount.cend(); ++it ) }
if (it ->second > currentMax) {
arg_max = it->first;
currentMax = it->second;
}
}
cout << "Value " << arg_max << " occurs " << currentMax << " times " << endl;
Another way to find the mode is to sort the vector and loop through it once, keeping track of the indices where the values change.
Here's a templated function based on Rob's excellent answer above.
template<typename KeyType, typename ValueType>
std::pair<KeyType,ValueType> get_max( const std::map<KeyType,ValueType>& x ) {
using pairtype=std::pair<KeyType,ValueType>;
return *std::max_element(x.begin(), x.end(), [] (const pairtype & p1, const pairtype & p2) {
return p1.second < p2.second;
});
}
Example:
std::map<char,int> x = { { 'a',1 },{ 'b',2 },{'c',0}};
auto max=get_max(x);
std::cout << max.first << "=>" << max.second << std::endl;
Outputs: b=>2