国际原油指数

** 数据框 ** 1.许多数据集是以数据框的形式出现。 2.一个数据框就是将许多向量组合起来的一个对象，它是二维的，通常 其列表示变量, 其行表示观测 ， 显示数据框时左侧会显示观测值的序号。 建立数据框的函数 若数据本身保存在一个文件中, 则通过读取该文件建立数据框 read.table() 可以读取txt文件 R无法读取excel直接保存文件，应该文件——导出——csv格式保存 read.csv() 先将数据另存为带逗号的数据(Comma Seperated values) read.delim() 先将数据另存为用tab作为分界符的数据 注：若数据集很大(如1,000,000观测x200变量)，则可由ODBC联接由数据库读入. 导入外部数据示例 建立如下数据，保存在 C:\Users\我\Desktop\example.csv 中 （RGui可读取有中文的文件） ！！需使用 / 注意！！ header=T，导入数据第一行标题 data=read.csv(“C:/Users/我/Desktop/example.csv”,header=T) data y x 1 3 13 2 5 24 3 2 6 4 7 21 5 9 26 更快捷的打开方式！ file.choose() data=read.csv(file.choose()) data y x 1 3 13 2 5 24 3

凉肝的题解 A. Mezo Playing Zoma Input Output Example Note 题解 B. Just Eat It! Input Output Example Note 题解 C. Fadi and LCM Input Output Examples 题解 D. Dr. Evil Underscores Input Output Examples Note 题解 E. Deadline Input Output Example Note 题解 F. Yet Another Meme Problem Input Output Example 题解 G. HQ9+ Input Output Examples Note 题解 H. Rolling The Polygon Input Output Example 题解 A. Mezo Playing Zoma Today, Mezo is playing a game. Zoma, a character in that game, is initially at position x=0. Mezo starts sending n commands to Zoma. There are two possible commands: ‘L’ (Left) sets the position x:=x−1; ‘R

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: i have this 8 question survey in my mobile application handover project. At first the corona did not prompt me any error message and the app works just fine but when i add 2 more question to it i start getting this message error i am not sure why the error is "a nil value" but my code look something like this.(line 662 to 678) function checkEBASComplete() local tempScore = 0 for i = 1, 10 do print("EBAS:"..ebasRating_Arr[i]) tempScore = tempScore + ebasRating_Arr[i] if (ebasRating_Arr[i] == -1) then ebasScore = 0 ebasScore_text.text = "Test

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I know that in more recent Java versions string concatenation String test = one + "two"+ three; Will get optimized to use a StringBuilder . However will a new StringBuilder be generated each time it hits this line or will a single Thread Local StringBuilder be generated that is then used for all string concatenation? In other words can I improve on the performance for a frequently called method by creating my own thread local StringBuilder to re-use or will there be no significant gains by doing so? I can just write a test for this but I

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: For IGF data from nlme library, I'm getting this error message: lme(conc ~ 1, data=IGF, random=~age|Lot) Error in lme.formula(conc ~ 1, data = IGF, random = ~age | Lot) : nlminb problem, convergence error code = 1 message = iteration limit reached without convergence (10) But everything is fine with this code lme(conc ~ age, data=IGF) Linear mixed-effects model fit by REML Data: IGF Log-restricted-likelihood: -297.1831 Fixed: conc ~ age (Intercept) age 5.374974367 -0.002535021 Random effects: Formula: ~age | Lot Structure: General positive

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I'm using the -com.apple.CoreData.ConcurrencyDebug argument on launch to debug concurrency in my CoreData app. During app launch, I perform an asynchronous fetch on the main thread's managed object context. // set up the async request NSError * error = nil; [MOC executeRequest:asyncFetch error:&error]; if (error) { NSLog(@"Unable to execute fetch request."); NSLog(@"%@, %@", error, error.localizedDescription); } This code is called from the main thread, but executeRequest: enqueues it to another thread, which I understand to be the correct

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: In which case using objects like numpy.r_ or numpy.c_ is better (more efficient, more suitable) than using fonctions like concatenate or vstack for example ? I am trying to understand a code where the programmer wrote something like: return np.r_[0.0, 1d_array, 0.0] == 2 where 1d_array is an array whose values can be 0, 1 or 2. Why not using np.concatenate (for example) instead ? Like : return np.concatenate([[0.0], 1d_array, [0.0]]) == 2 It is more readable and apparently it does the same thing. 回答1: np.r_ is implemented in the numpy/lib

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I am concatenating two mp4 videos. The problem is that first video (intro.mp4) lasts 5 seconds, second video (output.mp4) lasts 2 seconds and video created by concatenating them lasts 9 seconds (and should last 5+2 = 7 seconds). In final.mp4 video the last frame from first video (intro.mp4) i shown for additional 2 seconds before second video (output.mp4) is played. It looks like a lag when watching video. What I am doing wrong? list.txt: file 'data/intro.mp4' file 'output.mp4' command: ./bin/ffmpeg -f concat -i list.txt -c copy final.mp4

HashTable 内部数据结构是数组+链表，键值对不允许为null，线程安全，但是锁是整表锁，性能较差/效率低 HashMap 结构同HashTable，键值对允许为null，线程不安全， 默认初始大小为16（固定为2的幂次方）， 默认扩容阀值为0.75，扩容方式为，先插入再扩容，所以会产生无效扩容， 单个链表长度默认为8，当超过时链表自动转为红黑树结构，当树结构长度小于6时，重新转为链表 ConcurrentHashMap jdk1.5之后对HashTable的升级版，性能效率各方面都有巨大的提升， 在1.5-1.7版本中使用segment作为分割单元，操作过程中会锁住segment，默认初始为16个segment，采用的是可重入锁ReentrantLock 在1.8之后放弃segment，采用与HashMap相同的数据结构，Node，采用CAS机制类似乐观锁，使用3个CAS操作来确保node的一些操作的原子性，这种方式代替了锁，减小了锁的粒度，来增强并发性能

一、concurrent模块的介绍 concurrent.futures 模块提供了高度封装的异步调用接口 ThreadPoolExecutor： 线程池，提供异步调用 ProcessPoolExecutor： 进程池，提供异步调用 ProcessPoolExecutor 和 ThreadPoolExecutor： 两者都实现相同的接口，该接口由抽象Executor类定义。 二、基本方法 submit(fn, *args, **kwargs): 异步提交任务 map(func, *iterables, timeout=None, chunksize=1) ：取代for循环submit的操作 shutdown(wait=True) ：相当于进程池的 pool.close()+pool.join() 操作 wait=True，等待池内所有任务执行完毕回收完资源后才继续 wait=False，立即返回，并不会等待池内的任务执行完毕 但不管wait参数为何值，整个程序都会等到所有任务执行完毕 submit和map必须在shutdown之前 result(timeout=None) ：取得结果 add_done_callback(fn) ：回调函数 三、进程池和线程池 池的功能：限制进程数或线程数. 什么时候限制： 当并发的任务数量远远大于计算机所能承受的范围,即无法一次性开启过多的任务数量