Boost irange should really be the answer (ThxPaul Brannan) I’m adding my answer to provide a compelling example of very valid use-cases that are not served well by manual looping: #include <boost/range/adaptors.hpp> #include <boost/range/algorithm.hpp> #include <boost/range/irange.hpp> using namespace boost::adaptors; static int mod7(int v) { return v % 7; } int main() { std::vector<int> v; boost::copy( … Read more
You need to use an explicit java.util.Iterator to iterate over the Map‘s entry set rather than being able to use the enhanced For-loop syntax available in Java 6. The following example iterates over a Map of Integer, String pairs, removing any entry whose Integer key is null or equals 0. Map<Integer, String> map = … … Read more
If you can, find and read “The C++ Standard Library: A Tutorial and Reference”. This book contains a whole chapter about STL iterators. Here is a little something from the book: Iterator Category Ability Providers —————– ——————————- —————————- Input iterator Reads forward istream Output iterator Writes forward ostream, inserter Forward iterator Reads/writes forward forward_list, unordered_[multi]set, … Read more
You can use the izip!() macro from the crate itertools, which implements this for arbitrary many iterators: use itertools::izip; fn main() { let a = [1, 2, 3]; let b = [4, 5, 6]; let c = [7, 8, 9]; // izip!() accepts iterators and/or values with IntoIterator. for (x, y, z) in izip!(&a, &b, … Read more
for-each is syntactic sugar for using iterators (approach 2). You might need to use iterators if you need to modify collection in your loop. First approach will throw exception. for (String i : list) { System.out.println(i); list.remove(i); // throws exception } Iterator it=list.iterator(); while (it.hasNext()){ System.out.println(it.next()); it.remove(); // valid here }
std::advance( iter, 2 ); This method will work for iterators that are not random-access iterators but it can still be specialized by the implementation to be no less efficient than iter += 2 when used with random-access iterators.
They are iterable, but they are not iterators. They can be passed to iter() to get an iterator for them either implicitly (e.g. via for) or explicitly, but they are not iterators in and of themselves.
One argument that is repeated, one argument in c from itertools import repeat for result in executor.map(f, repeat(a), c): pass Need to unpack items of c, and can unpack c from itertools import izip for result in executor.map(f, *izip(*c)): pass Need to unpack items of c, can’t unpack c Change f to take a single … Read more
Using Guava library: int size = Iterators.size(iterator); Internally it just iterates over all elements so its just for convenience.
if any(True for _ in iterator): print(‘iterator had at least one element’) if all(False for _ in iterator): print(‘iterator was empty’) Note that this will consume the first element of the iterable if it has at least one element.