TL;DR go directly to the final example I’ll try and recap. Definitions The for comprehension is a syntax shortcut to combine flatMap and map in a way that’s easy to read and reason about. Let’s simplify things a bit and assume that every class that provides both aforementioned methods can be called a monad and … Read more
Assuming this is what you meant: // traditional for loop for (int i = 0; i < collection.size(); i++) { T obj = collection.get(i); // snip } // using iterator Iterator<T> iter = collection.iterator(); while (iter.hasNext()) { T obj = iter.next(); // snip } // using iterator internally (confirm it yourself using javap -c) for … Read more
Almost. for(; iter != endIter; ) { if (Some Condition) { iter = aMap.erase(iter); } else { ++iter; } } What you had originally would increment the iterator twice if you did erase an element from it; you could potentially skip over elements that needed to be erased. This is a common algorithm I’ve seen … Read more
All that is required of the key is that it be copiable and assignable. The ordering within the map is defined by the third argument to the template (and the argument to the constructor, if used). This defaults to std::less<KeyType>, which defaults to the < operator, but there’s no requirement to use the defaults. Just … Read more
List<Value> list = new ArrayList<Value>(map.values()); assuming: Map<Key,Value> map;
You can use JSTL <c:forEach> tag to iterate over arrays, collections and maps. In case of arrays and collections, every iteration the var will give you just the currently iterated item right away. <%@ taglib prefix=”c” uri=”http://java.sun.com/jsp/jstl/core” %> <c:forEach items=”${collectionOrArray}” var=”item”> Item = ${item}<br> </c:forEach> In case of maps, every iteration the var will give … Read more
You need to give a comparison functor to the map otherwise it’s comparing the pointer, not the null-terminated string it points to. In general, this is the case anytime you want your map key to be a pointer. For example: struct cmp_str { bool operator()(char const *a, char const *b) const { return std::strcmp(a, b) … Read more
You’re in object denial. You should use an object that holds the number, name, address, phone (maybe you could call it ContactInformation) and put that into the map.
The shortest answer I know of that uses only the standard library is map1 ++ map2.map{ case (k,v) => k -> (v + map1.getOrElse(k,0)) }
The standard associative-container erase idiom: for (auto it = m.cbegin(); it != m.cend() /* not hoisted */; /* no increment */) { if (must_delete) { m.erase(it++); // or “it = m.erase(it)” since C++11 } else { ++it; } } Note that we really want an ordinary for loop here, since we are modifying the container … Read more