set

Memory consumption of a list and set in Python

由 人走茶凉 提交于 2020-03-21 18:04:05
问题 >>> from sys import getsizeof >>> a=[i for i in range(1000)] >>> b={i for i in range(1000)} >>> getsizeof(a) 9024 >>> getsizeof(b) 32992 My question is, why does a set consume so much more memory compared to a list? Lists are ordered, sets are not. Is it an internal structure of a set that consumes memory? Or does a list contain pointers and set does not? Or maybe sys.getsizeof is wrong here? I've seen questions about tuples, lists and dictionaries, but I could not find any comparison between

Can php PDO fetch two results sets? And If yes, what is better 1 result set or more than 1?

由 為{幸葍}努か 提交于 2020-03-18 06:49:11
问题 If is posible, how can I fetch two results sets: $sth=$dbh->prepare("SELECT * FROM tb1 WHERE cond1; SELECT * from tb2 Where cond2"); $sth->execute(); $row=$sth->fetchAll(); print_r ($row); These are two completely different tables (no fiels in common). 回答1: Yes PDO can fetch two (or more) rowsets, as long as the database you are using supports it. I think MS SQL Server and MySQL both support this functionality, but at the time of writing SQLite does not. The function you want is PDOStatement:

python reduce to find the union of sets

由 怎甘沉沦 提交于 2020-03-15 21:56:30
问题 I am trying to find the union of set of sets. Specifically I want the union of the list of nodes for each key in the dictionary of networkx graphs called periodic_gs . I would like to use the reduce function as it seems reasonable to take the union of all periodic_gs[x].nodes() where x is a key of periodic_gs . Here is my attempt: reduce(lambda x,y: set(periodic_gs[x].nodes()).union(set(periodic_gs[y].nodes())), periodic_gs.keys(), {}) To me, this says take the union of the nodes across each

python reduce to find the union of sets

由 情到浓时终转凉″ 提交于 2020-03-15 21:56:21
问题 I am trying to find the union of set of sets. Specifically I want the union of the list of nodes for each key in the dictionary of networkx graphs called periodic_gs . I would like to use the reduce function as it seems reasonable to take the union of all periodic_gs[x].nodes() where x is a key of periodic_gs . Here is my attempt: reduce(lambda x,y: set(periodic_gs[x].nodes()).union(set(periodic_gs[y].nodes())), periodic_gs.keys(), {}) To me, this says take the union of the nodes across each

Build a set fails when using set(int) (Python)

由 时光毁灭记忆、已成空白 提交于 2020-03-15 05:35:08
问题 I can do >>> s = {1} >>> type(s) <class 'set'> but >>> s = set(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not iterable what is the difference? 回答1: The difference is that the set() constructor takes an iterable. A single number is not an iterable. s = set((1,)) 来源： https://stackoverflow.com/questions/27180659/build-a-set-fails-when-using-setint-python

Build a set fails when using set(int) (Python)

由 廉价感情. 提交于 2020-03-15 05:34:55
问题 I can do >>> s = {1} >>> type(s) <class 'set'> but >>> s = set(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not iterable what is the difference? 回答1: The difference is that the set() constructor takes an iterable. A single number is not an iterable. s = set((1,)) 来源： https://stackoverflow.com/questions/27180659/build-a-set-fails-when-using-setint-python

Build a set fails when using set(int) (Python)

由 谁说胖子不能爱 提交于 2020-03-15 05:34:32
问题 I can do >>> s = {1} >>> type(s) <class 'set'> but >>> s = set(1) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'int' object is not iterable what is the difference? 回答1: The difference is that the set() constructor takes an iterable. A single number is not an iterable. s = set((1,)) 来源： https://stackoverflow.com/questions/27180659/build-a-set-fails-when-using-setint-python

How do I add two sets

由 社会主义新天地 提交于 2020-03-13 05:34:05
问题 a = {'a','b','c'} b = {'d','e','f'} I want to add above two set values. Need output like, c = {'a','b','c','d','e','f'} 回答1: All you have to do to combine them is c = a|b . Sets are unordered sequences of unique values. a|b is the union of the two sets (a new set with all values found in either set). This is a class of operation called a "set operation", which sets provide convenient tools for. 回答2: You can use update() to combine set(b) into set(a) Try to this. a = {'a', 'b', 'c'} b = {'d',

Making a sequence of tuples unique by a specific element

由 无人久伴 提交于 2020-03-08 08:55:49
问题 So I have a tuple of tuples a = ((1, 2), (7, 2), (5, 2), (3, 4), (8, 4)) I would like to remove all the tuples from 'a' which have the a common second element, except for one (any one of them). For the example above I would like the new output a = ((1,2),(3,4)) In other words I would like to eliminate tuples which are considered duplicate elements in the second position of the tuple. I would like to know the most efficient way to achieve this, and also like to know if I can do the same with

集合类操作优化经验总结(二)

由 …衆ロ難τιáo~ 提交于 2020-03-06 18:20:54
集合类介绍 LinkedList 类 LinkedList 实现了 List 接口，允许 Null 元素。此外 LinkedList 提供额外的 Get、Remove、Insert 等方法在 LinkedList 的首部或尾部操作数据。这些操作使得 LinkedList 可被用作堆栈（Stack）、队列（Queue）或双向队列（Deque）。请注意 LinkedList 没有同步方法，它不是线程同步的，即如果多个线程同时访问一个 List，则必须自己实现访问同步。一种解决方法是在创建 List 时构造一个同步的 List，方法如 List list = Collections.synchronizedList(new LinkedList(...))； ArrayList 类 ArrayList 实现了可变大小的数组。它允许所有元素，包括 Null。Size、IsEmpty、Get、Set 等方法的运行时间为常数，但是 Add 方法开销为分摊的常数，添加 N 个元素需要 O(N) 的时间，其他的方法运行时间为线性。 每 个 ArrayList 实例都有一个容量（Capacity），用于存储元素的数组的大小，这个容量可随着不断添加新元素而自动增加。当需要插入大量元素时，在插入前可以调用 ensureCapacity 方法来增加 ArrayList 的容量以提高插入效率。和
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