mean

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 R, I want to summarize my data after grouping it based on the runs of a variable x (aka each group of the data corresponds to a subset of the data where consecutive x values are the same). For instance, consider the following data frame, where I want to compute the average y value within each run of x : (dat In this example, the x variable has runs of length 3, then 2, then 1, and finally 1, taking values 1, 2, 1, and 2 in those four runs. The corresponding means of y in those groups are 2, 4.5, 6, and 7. It is easy to carry out this

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: What is BODMAS and why is it useful in programming? 回答1: http://www.easymaths.com/What_on_earth_is_Bodmas.htm : What do you think the answer to 2 + 3 x 5 is? Is it (2 + 3) x 5 = 5 x 5 = 25 ? or 2 + (3 x 5) = 2 + 15 = 17 ? BODMAS can come to the rescue and give us rules to follow so that we always get the right answer: (B)rackets (O)rder (D)ivision (M)ultiplication (A)ddition (S)ubtraction According to BODMAS, multiplication should always be done before addition, therefore 17 is actually the correct answer according to BODMAS and will also be

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: There are other posts about row-wise operators on datatable. They are either too simple or solves a specific scenario My question here is more generic. There is a solution using dplyr. I have played around but failed to find a an equivalent solution using data.table syntax. Can you please suggest an elegant data.table solution that reproduce the same results than the dplyr version? EDIT 1 : Summary of benchmarks of the suggested solutions on real dataset (10MB, 73000 rows, stats made on 24 numeric columns). The benchmark results is

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 a list of lists with the following structure: > mylist <- list(list(a=as.numeric(1:3), b=as.numeric(4:6)), list(a=as.numeric(6:8), b=as.numeric(7:9))) > str(mylist) List of 2 $ :List of 2 ..$ a: num [1:3] 1 2 3 ..$ b: num [1:3] 4 5 6 $ :List of 2 ..$ a: num [1:3] 6 7 8 ..$ b: num [1:3] 7 8 9 I would like to get the element-wise mean between the vectors a and b of mylist . For the vector a , the result would be this: > a [1] 3.5 4.5 5.5 I know the functions lapply , rbind and colMeans but I can't solve the problem with them. How can 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: I have written a model in Keras (with theano backend) and compile my model like this: model.compile(Adam(0.001), loss='mse', metrics=['mse', 'mae']) , i.e. my objective loss function is mean squared error and the metrics to report are mean squared error and mean absolute error . Then I run my model: model.fit(X_train, y_train, nb_epoch=500, validation_data=(X_test, y_test)) Keras reports results as: Epoch 500/500: 0s - loss: 5.5990 - mean_squared_error: 4.4311 - mean_absolute_error: 0.9511 - val_loss: 7.5573 - val_mean_squared_error: 6.3877

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: This question already has an answer here: Use mean in ggplot boxplots instead of median 1 answer How to plot mean and standard error in Boxplot in R 2 answers Changing whisker definition in geom_boxplot 3 answers for some inane reason, I need to create a boxplot where the middle line is the mean instead of the median. I checked stackoverflow already and found examples of adding a mean line, but not exactly what I need. I tried using stat_smooth but no dice. Any ideas? code below: dust <- c(4.5, 3.7, 5, 5.2, 8.5, 6.6, 4.7, 5, 5.7, 4.3, 2.3, 7

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 found some code written in Swift on github , And get a little confused about this line var done: (NSError?, NSData, NSString?) -> () = { (_, _, _) -> () in } could you please explain the real meaning of this line? Thank you very much! 回答1: _ means don't name that thing. It can be used in a number of places. In your case, it is saying ignore the variable being passed into the closure. The code you gave is ignoring all parameters but you can also just ignore some parameters. in is the start of the implementation of the closure. In your

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: So I saw a talk called rand() Considered Harmful and it advocated for using the engine-distribution paradigm of random number generation over the simple std::rand() plus modulus paradigm. However, I wanted to see the failings of std::rand() firsthand so I did a quick experiment: Basically, I wrote 2 functions getRandNum_Old() and getRandNum_New() that generated a random number between 0 and 5 inclusive using std::rand() and std::mt19937 + std::uniform_int_distribution respectively. Then I generated 960,000 (divisible by 6) random numbers

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 was testing some code on Visual Studio 2008 and noticed security_cookie . I can understand the point of it, but I don't understand what the purpose of this instruction is. rep ret /* REP to avoid AMD branch prediction penalty */ Of course I can understand the comment :) but what is this prefix exaclty doing in context with the ret and what happens if ecx is != 0? Apparently the loop count from ecx is ignored when I debug it, which is to be expected. The code where I found this was here (injected by the compiler for security): void _

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: print >> sys.stderr, "Error in atexit._run_exitfuncs:" Why print '>>' in front of sys.stderr ? Thanks. 回答1: This syntax means writes to a file object ( sys.stderr in this case) instead of standard output. [Link] In Python 3.0, print becomes a function instead of a statement: [Link] print("Error in atexit._run_exitfuncs:", file=sys.stderr) 回答2: From the Python documentation : print also has an extended form, defined by the second portion of the syntax described above. This form is sometimes referred to as “print chevron.” In this form, the