In a function, I want to generate a list of numbers in range: (This function will be called only once when executing the program.)
void DataSet::finalize(double trainPercent, bool genValidData)
{
srand(time(0));
printf("%d\n", rand());
// indices = {0, 1, 2, 3, 4, ..., m_train.size()-1}
vector<size_t> indices(m_train.size());
for (size_t i = 0; i < indices.size(); i++)
indices[i] = i;
random_shuffle(indices.begin(), indices.end());
// Output
for (size_t i = 0; i < 10; i++)
printf("%ld ", indices[i]);
puts("");
}
The results are like:
850577673
246 239 7 102 41 201 288 23 1 237
After a few seconds:
856981140
246 239 7 102 41 201 288 23 1 237
And more:
857552578
246 239 7 102 41 201 288 23 1 237
Why the function rand()
works properly but `random_shuffle' does not?
random_shuffle()
isn't actually specified to use rand()
and so srand()
may not have any impact. If you want to be sure, you should use one of the C++11 forms, random_shuffle(b, e, RNG)
or shuffle(b, e, uRNG)
.
An alternative would be to use random_shuffle(indices.begin(), indices.end(), rand());
because apparently your implementation of random_shuffle()
is not using rand()
.
来源:https://stackoverflow.com/questions/22496942/stdrandom-shuffle-produce-the-same-result-even-though-srandtime0-called-on