Question

How to calculate the median of a digital number array has been discussed before. For example, you can refer to What is the right approach when using STL container for median calculation?. Now I have a different question, and that is how can you get the index of the median in the original STL container. In order to illustrate my question, I give an example:

vector<int> myarray;
myarray.push_back(3);
myarray.push_back(1);
myarray.push_back(100);
myarray.push_back( 20);
myarray.push_back(200);
int n = myarray.size()/2;
nth_element(myarray.begin(), myarray.begin()+n, myarray.end());
int median = myarray[n];

In the above codes I can get the median value but I can not get its index in the original vector array (4). Any ideas? Thanks!

Answer 1

If it is accapteble to search the element

vector<int>::iterator itOfMedian = std::find(myarray.begin(), myarray.end(), median);
int index = itOfMedian - myarray.begin();

should do the trick.

EDIT

seems you have point here. nth_element sorts its argument vector… Therefore

vector<int> myArrayCopy = myarray;
// find median in myArrayCopy
vector<int>::iterator itOfMedian = std::find(myarray.begin(), myarray.end(), median);
int index = itOfMedian - myarray.begin();