insert in a vector of vector

[mickey]

hi I'm trying to do this:


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;

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

[wysota]

Can't you use std::shuffle?

[mickey]

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

[danadam]

vector < vector <double> > temp;
temp.resize(_set->size());
vector < vector <double> >::iterator iit=temp.begin();
What is this iterator for? You only increase it in your loop, but you don't use it anywhere.


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);
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().



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