如何在 dplyr 中正确设置排列和分组？

Question

我的数据结构如下：

Athletes = c("Gus", "Hudson", "Bobby", "Tom")
set.seed(400)
RawData <- data.frame(Name = rep((Athletes), each = 400),
                                Quarter = as.numeric(rep(1:4, each = 100)),
                                Sample = as.numeric(rep(1:100, each = 1)),
                                X = runif(400, 26, 30), 
                                Y = runif(400, 12, 16))

我希望为每个Athlete 每个Sample 每个Quarter 计算每个X 和Y 对的位移。为此，我设置了以下代码：

DistanceOutput <- RawData %>%
  arrange(Name, Sample, Quarter) %>%
  group_by(Name, Quarter) %>%
  mutate( lagX = lag(X, order_by=Sample), lagY = lag(Y, order_by=Sample)) %>%
  rowwise() %>%
  mutate(Distance = dist( matrix( c(X,Y,lagX,lagY),nrow=2,byrow=TRUE) )) %>%
  select(-lagX, -lagY)

但是，这会返回一个data.frame，其结构如下：

> head(DistanceOutput, n=10)
Source: local data frame [10 x 6]

     Name Quarter Sample        X        Y Distance
   (fctr)   (dbl)  (dbl)    (dbl)    (dbl)    (dbl)
1   Bobby       1      1 27.82656 13.85830       NA
2   Bobby       2      1 27.37298 15.67940       NA
3   Bobby       3      1 28.74274 12.25703       NA
4   Bobby       4      1 26.63564 13.07924       NA
5   Bobby       1      2 26.32446 12.64722 1.929508
6   Bobby       2      2 26.88957 14.52096       NA
7   Bobby       3      2 27.53932 15.57959 3.533781
8   Bobby       4      2 28.03031 12.70763 1.443328
9   Bobby       1      3 29.68239 13.82739 3.559287
10  Bobby       2      3 29.43869 12.60890 3.186531

相反，我希望我的数据设置如下：

> head(DistanceOutput, n=3)
    Source: local data frame [10 x 6]

         Name Quarter Sample        X        Y Distance
       (fctr)   (dbl)  (dbl)    (dbl)    (dbl)    (dbl)
    1   Bobby       1      1 27.82656 13.85830       NA
    2   Bobby       1      2 26.32446 12.64722 1.929508
    3   Bobby       1      3 29.68239 13.82739 3.559287

我如何正确设置 group_by 并在 dplyr 中安排语句以正确反映我想要的输出？

谢谢。

Answer 1

我猜这是一个订单问题

DistanceOutput %>% 
         arrange(Name, Quarter, Sample) %>%
         head(3)
#   Name Quarter Sample        X        Y Distance
# <fctr>   <dbl>  <dbl>    <dbl>    <dbl>    <dbl>
#1  Bobby       1      1 28.40293 15.40195       NA
#2  Bobby       1      2 26.33676 14.32382 2.330544
#3  Bobby       1      3 28.60779 14.67457 2.297951