What C++ container should I choose for frequency graph? - c++

Question

I have a little project. I want to make a frequency graph something like this:
a-axis
3| x
2|` x x
1| x x x
0| x x x x
|`_____________`
2 4 6 7 9 b-axis
What container should I use and how do go about implementing that in the simplest way.
The container should also record zero value (frequency).
I find it difficult to correct implement the container. Is there are any sample code I can look at? Or anybody can write a sample for me to study here.
Update:
I was thinking of making std::map<int,std::vector<int>> keyAndMap
How do I access the vector which is inside keyAndMap?
Because I somehow can't do keyAndMap.insert(std::make_pair<int,std::vector<int>>(bAxis,bVec.push_back(bValue)));
The main problem I think is how to generate unique vector for each key in std::map?
const int tries = 21;
std::vector<int>values;
std::map<int,std::vector<int>>keyAndMap;
for (int i = 1; i < tries; i++)
{
int n = i;
int cycle = calculate(n);
/*This next line is an error... why?*/
keyAndMap.insert(std::make_pair<int,std::vector<int>>(cycle,values.push_back(i)));
}
although if i somehow got through that line, my logic here is flawed because the vector is not unique to each key.
Each 'x' in the little pretty graph i drew is gained with each pass in the loop.
So for each b-axis (2,4,6,7, and 9) should be in their own std::vector

Answer 1

What container should I use and how do go about implementing that in the simplest way?
A possible container would be a std::map<key, frequency>, both of which are of type int, with the additional advantage of your values being sorted. Then you could simply read values by something like:
std::map<int, int> data;
int key;
while (std::cin >> key)
{
++data[key]; // increment the frequency of a given key*
}
To access the data you could use iterators, like so:
for (auto it = data.begin; it != data.end(); ++it)
{
// iterator to key
std::cout << it->first <<": "<< it->second <<"\n";
// iterator to frequency
}
Which will print a two-column table of your data.
Second, even simpler approach:
You could use a std::vector<frequency>, where frequency is of type int, and your data would be the indexes of the std::vector, however, you should know the range** of your data so that you can use it as an initial vector size:
i.e. std::vector<int> data(5, 0) could hold values with range 5.
Then if, for example, your data is consisted of the integers: [0, 4], you could have:
std::vector<int> data(5, 0); // five elements with initial value 0
int key;
while(std::cin >> key) // assuming key >= 0 && key < 5
{
data[key] += 1;
}
and then print with:
for (int i= 0; i < data.size(); ++i)
{
std::cout << i <<": "<< data[i] <<"\n";
}
* The default initial frequency value of a distinct key is: 0, so you can simply use the key to access and increment an element.
**range - difference between the lowest and highest values.