本次美国代写主要为统计相关的限时测试

话题:
将有几个问题向您展示一些代码,并询问您运行代码时*会发生什么*以及*为什么* R产生输出。您可以使用 R 来确定代码将输出什么。如果问题问为什么,一定要回答为什么。

例如,涵盖第 1-1 课材料的问题可以是:
> x <- c(NA, NULL)
> y <- c(NA, 字符(0))

下面的代码会返回什么?如果他们返回不同的结果,为什么?
> 长度(x)
> 长度(y)

使用上面相同的 x 和 y 值,下面的代码将返回什么?如果他们回来
结果不同,为什么?
> is.logical(x)
> is.logical(y)

会有几个问题要求您编写几行代码来执行任务。问题将足够简单,因此可以用六行或更少的代码完成一个解决方案。这不是限制。

如果需要,您可以编写 20 行代码。这只是对问题复杂程度的描述。
对于这些问题,您将在文本框中编写代码。您应该先在 R Studio 中编写代码,然后在运行后,将代码复制到文本框。确保您只复制代码。

当我们为您的考试评分时,我们会将文本框中的代码复制到 R 中并运行它以对其进行评估。确保在复制时不包括诸如 + 或 > 或 # 之类的杂散符号,这些符号有时位于行前。如果它产生错误,您将不会因提交而获得积分。

示例问题:我可能会向您展示数据集的头部,并会要求您使用 tidyr 和/或 dplyr 来重塑数据框并按组提供汇总统计信息。
另一个例子:我可能会提供一个网站的 url,并要求您提供提取某些项目所需的代码。

Topics:
There will be several questions showing you some code and asking you *what* will happen when we run the code and *why* R produces the output. You are allowed to use R to figure out what the code will output. If the question asks why, be sure to answer why.

For example, a question covering material from Lecture 1-1 could be:
> x <- c(NA, NULL)
> y <- c(NA, character(0))

What will the following code return? If they return different results, why?
> length(x)
> length(y)

Using the same values of x and y from above, what will the following code return? If they return
different results, why?
> is.logical(x)
> is.logical(y)

There will be several questions asking you to write a few lines of code to perform a task. Questions will be simple enough so that a solution can be done with six lines of code or less. This is not a restriction.

You can write twenty lines of code if you need to. This is simply a description of the level of complexity of the problems.
For these questions, you will write your code in a textbox. You should write the code in R Studio first and after you get it working, you will copy your code over to the textbox. Make sure you only copy the code.

When we grade your exam, we will copy the code from the textbox into R and run it to evaluate it. Make sure you do not include stray symbols like + or > or # that sometimes precedes lines when you copy it. If it produces errors, you will not get points for your submission.

Example problem: I might show you the head of dataset and will ask you to use tidyr and/or dplyr to reshape the data frame and provide summary statistics by group.
Another example: I might provide the url of a website and ask you for the code needed to extract certain items.

 


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