insert in a vector of vector

hi I'm trying to do this:

Code:

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vector < vector <double> > temp;
	temp.resize(_set->size());	
	vector < vector <double> >::iterator iit=temp.begin();
	int i=0;
	vector < vector <double> >::iterator itra = _set->begin();	
	srand ((unsigned)time(NULL));
	while ( ! _set->empty() )  {
		do {
			i = rand() % (int) _set->size();
			cout << " i " << i << endl; 
			if (i == 0 &&  _set->size() == 1) break;
		} while (i >= (int) _set->size() || i == 0);
		temp.insert (temp.begin(), itra+i, itra+i); 	//here it is filling 	nothing
		int dist = (int) distance (_set->begin(), _set->begin()+i);
		_set->erase(itra+dist);
		++iit;
	}
	 *_set = temp;

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my aim is take my vec of vec and shuffle its elements (its vectors).
Before chose a vector of _set at random, put it at begin of temp and erase it from _set; I've been trying this way and it seems me more difficult...
the calcolus of 'i' is ok. but insert doesn't work.
Can anyone help me?
thanks

Can't you use std::shuffle?

I didn't know it; thanks. But some hints to understand the wrong behavoir of my code ? (ie why insert don't work?)

Quote:

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Code:

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vector < vector <double> > temp;
temp.resize(_set->size());	
vector < vector <double> >::iterator iit=temp.begin();

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What is this iterator for? You only increase it in your loop, but you don't use it anywhere.

Quote:

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Code:

---

int i=0;
vector < vector <double> >::iterator itra = _set->begin();	
srand ((unsigned)time(NULL));
while ( ! _set->empty() )  {
	do {
		i = rand() % (int) _set->size();
		cout << " i " << i << endl; 
		if (i == 0 &&  _set->size() == 1) break;
	} while (i >= (int) _set->size() || i == 0);

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These conditions are redundant, I guess. By using % operator variable "i" takes value from interval 0 (incl), set->size()(excl). So if size is 1 then it's no use checking if "i" is zero. Additionally variable "i" will never be greater or equal then set->size().

Quote:

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Code:

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temp.insert (temp.begin(), itra+i, itra+i); 	//here it is filling nothing

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These two iterators points the same element. insert() method insert sequence from first(incl) to last(excl), so in your case it inserts nothing. Try to pass the last argument as itra+i+1.