>>> x = 42 >>> xs = [1, 2, 3] >>> xs.insert(0, x) >>> xs [42, 1, 2, 3] How it works: list.insert(index, value) Insert an item at a given position. The first argument is the index of the element before which to insert, so xs.insert(0, x) inserts at the front of the list, and … Read more
String.join With Java 8 you can do this without any third party library. If you want to join a Collection of Strings you can use the String.join() method: List<String> list = Arrays.asList(“foo”, “bar”, “baz”); String joined = String.join(” and “, list); // “foo and bar and baz” Collectors.joining If you have a Collection with another … Read more
The s.insert(0, x) form is the most common. Whenever you see it though, it may be time to consider using a collections.deque instead of a list. Prepending to a deque runs in constant time. Prepending to a list runs in linear time.
If your elements are value types, then you can just do: List<YourType> newList = new List<YourType>(oldList); However, if they are reference types and you want a deep copy (assuming your elements properly implement ICloneable), you could do something like this: List<ICloneable> oldList = new List<ICloneable>(); List<ICloneable> newList = new List<ICloneable>(oldList.Count); oldList.ForEach((item) => { newList.Add((ICloneable)item.Clone()); }); … Read more
It is rare, in reality, that you would want to use an array. Definitely use a List<T> any time you want to add/remove data, since resizing arrays is expensive. If you know the data is fixed length, and you want to micro-optimise for some very specific reason (after benchmarking), then an array may be useful. … Read more
Well, it would be easier to exclude them in the first place: authorsList = authorsList.Where(x => x.FirstName != “Bob”).ToList(); However, that would just change the value of authorsList instead of removing the authors from the previous collection. Alternatively, you can use RemoveAll: authorsList.RemoveAll(x => x.FirstName == “Bob”); If you really need to do it based … Read more
Given: xs = [‘1’, ‘2’, ‘3’] Use map then list to obtain a list of integers: list(map(int, xs)) In Python 2, list was unnecessary since map returned a list: map(int, xs)
Because [] and {} are literal syntax. Python can create bytecode just to create the list or dictionary objects: >>> import dis >>> dis.dis(compile(‘[]’, ”, ‘eval’)) 1 0 BUILD_LIST 0 3 RETURN_VALUE >>> dis.dis(compile(‘{}’, ”, ‘eval’)) 1 0 BUILD_MAP 0 3 RETURN_VALUE list() and dict() are separate objects. Their names need to be resolved, the … Read more
List<Value> list = new ArrayList<Value>(map.values()); assuming: Map<Key,Value> map;
To check for the presence of ‘abc’ in any string in the list: xs = [‘abc-123’, ‘def-456’, ‘ghi-789’, ‘abc-456’] if any(“abc” in s for s in xs): … To get all the items containing ‘abc’: matching = [s for s in xs if “abc” in s]