Perhaps, but this is a lovely example of the power of R.

". atan(y,x) returns"

My worry is that the reader would assume that atan(x,y) returns that angle.

Hadley defines this as

not_cancelled <- flights %>% 
  filter(!is.na(dep_delay), !is.na(arr_delay))

But in

flights %>% 
  filter(is.na(dep_time) | is.na(arr_time) | is.na(dep_delay) | is.na(arr_delay)) %>% 
select(sched_arr_time,arr_time,arr_delay,sched_dep_time,dep_time,dep_delay)

the first 6 flights have an NA only in arr_delay. Aren't these likely not to have been cancelled and simply have a missing data entry? Why isn't

not_cancelled <- flights %>%
filter(!is.na(dep_time), !is.na(arr_time))

a "better" definition?

Omit.

Another solution. Now that we know we can "trust" dep_delay we could simply

md <- flights %>%
select(carrier,flight,origin,dest,sched_dep_time,dep_time,dep_delay) %>%
arrange(min_rank(desc(dep_delay)))

There are no ties in the top 10.

If you wish, you could change this to "Eastern Daylight" to agree with its previous reference in that sentence.

I understand the point of the paragraph but this sentence is a bit unclear.

It's unclear to me what is intended here.

A nice analysis, showing the "messiness" of actual datasets.

Note that

select(flights,vars)

produces the same result.

*

December

Replace , by |.

Interestingly between microbenchmarks to 143 microseconds while >=, <= is 2.3 on my box!

Another interpretation:

colnames(flights)[colSums(is.na(flights)) > 0]

Elegant, at a 2x microbenchmark cost.

Do numerical operators execute faster than, say, %in%?

Omit

Must be na.rm = TRUE inside the sum parenthesis for the below graph to appear otherwise it will just be a blank graph.

By the way thanks so much for these solutions, they are extremely helpful and teach things which are not taught in the book!

There was no typo in the 2/2/19 version of r4ds.

Since the sum of x is the same across the input, couldn't you make the code less repetitive by assigning it to an intermediate variable?

sum_to_one <- function(x, na.rm = FALSE) { y = sum(x, na.rm = na.rm) x / y }

This should be arr_delay not dep_delay

这个膜运算选择了一个最大值

这个计算变量用的小技巧非常好，要深入体会一下

arrange也可以接受一个表达式生成的新变量然后根据这个新变量排序

这个是膜运算，类似于取余数，但是又不太一样，详细见：https://baike.baidu.com/item/%E5%8F%96%E6%A8%A1%E8%BF%90%E7%AE%97/10739384?fr=aladdin

这个不错，可以在对连续型变量转换成分类变量的时 候使用

通过两个变量排序，第一个生成一个逻辑变量T,F。因为缺失值是T，所以缺失值就排在了前边，然后再按照第二个变量dep_time排序

vertical

This should be "geom_jitter"

axes

position = "dodge2"

slightly changing

height = 0.4 and width =0.4 because the randomness is created on both negative and positive directions.