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
According to the manual: The key can either be an integer or a string. The value can be of any type. Additionally the following key casts will occur: Strings containing valid integers will be cast to the integer type. E.g. the key “8” will actually be stored under 8. On the other hand “08” will … Read more
I’m not positive what you’re asking, but if you’re looking for an example of when one would want to use a null key, I use them often in maps to represent the default case (i.e. the value that should be used if a given key isn’t present): Map<A, B> foo; A search; B val = … Read more
Functional approach: $array = array_filter($array, function($key) { return strpos($key, ‘foo-‘) === 0; }, ARRAY_FILTER_USE_KEY); Procedural approach: $only_foo = array(); foreach ($array as $key => $value) { if (strpos($key, ‘foo-‘) === 0) { $only_foo[$key] = $value; } } Procedural approach using objects: $i = new ArrayIterator($array); $only_foo = array(); while ($i->valid()) { if (strpos($i->key(), ‘foo-‘) === … Read more
Edit: As written in the comments the old code is not “best practice”. You should use a keygeneration algorithm like PBKDF2 with a high iteration count. You also should use at least partly a non static (meaning for each “identity” exclusive) salt. If possible randomly generated and stored together with the ciphertext. SecureRandom sr = … Read more
Use the fromkeys function to initialize a dictionary with any default value. In your case, you will initialize with None since you don’t have a default value in mind. empty_dict = dict.fromkeys([‘apple’,’ball’]) this will initialize empty_dict as: empty_dict = {‘apple’: None, ‘ball’: None} As an alternative, if you wanted to initialize the dictionary with some … Read more
Looks like you are using Python 3. In Python 3 dict.keys() returns an iterable but not indexable object. The most simple (but not so efficient) solution would be: vocab = list(fdist1.keys())[:200] In some situations it is desirable to continue working with an iterator object instead of a list. This can be done with itertools.islice(): import … Read more
ages = { ‘Bruce’ => 32, ‘Clark’ => 28 } mappings = { ‘Bruce’ => ‘Bruce Wayne’, ‘Clark’ => ‘Clark Kent’ } ages.transform_keys(&mappings.method(:[])) #=> { ‘Bruce Wayne’ => 32, ‘Clark Kent’ => 28 }
Just do a simple .keys() >>> dct = { … “1”: “a”, … “3”: “b”, … “8”: { … “12”: “c”, … “25”: “d” … } … } >>> >>> dct.keys() [‘1’, ‘8’, ‘3’] >>> for key in dct.keys(): print key … 1 8 3 >>> If you need a sorted list: keylist = dct.keys() … Read more
Make the value a list, e.g. a[“abc”] = [1, 2, “bob”] UPDATE: There are a couple of ways to add values to key, and to create a list if one isn’t already there. I’ll show one such method in little steps. key = “somekey” a.setdefault(key, []) a[key].append(1) Results: >>> a {‘somekey’: [1]} Next, try: key … Read more