使用 sparklyr 调用 collect_list 时保留基于另一个变量的顺序

Question

这个问题本质上是 this question 的重复，除了我在 R 中工作。pyspark 解决方案看起来很可靠，但我无法弄清楚如何将 collect_list 应用于相同的窗口函数在 sparklyr 中的方式。

我有一个具有以下结构的 Spark DataFrame：

------------------------------
userid |     date     | city
------------------------------
   1   |  2018-08-02  |   A
   1   |  2018-08-03  |   B
   1   |  2018-08-04  |   C
   2   |  2018-08-17  |   G
   2   |  2018-08-20  |   E
   2   |  2018-08-23  |   F

我正在尝试按userid 对DataFrame 进行分组，按date 对每个组进行排序，并将city 列折叠成其值的串联。期望的输出：

------------------
userid | cities
------------------
   1   |  A, B, C
   2   |  G, E, F

问题在于，我尝试使用的每种方法都导致一些用户（在对 5000 名用户的测试中约为 3%）的“城市”列的顺序不正确。

---

尝试 1：使用 dplyr 和 collect_list。

my_sdf %>%
  dplyr::group_by(userid) %>%
  dplyr::arrange(date) %>%
  dplyr::summarise(cities = paste(collect_list(city), sep = ", ")))

尝试2：使用replyr::gapply，因为该操作符合“Grouped-Order-Apply”的描述。

get_cities <- . %>%
   summarise(cities = paste(collect_list(city), sep = ", "))

my_sdf %>%
  replyr::gapply(gcolumn = "userid",
                 f = get_cities,
                 ocolumn = "date",
                 partitionMethod = "group_by")

尝试 3：编写为 SQL 窗口函数。

my_sdf %>% 
  spark_session(sc) %>%
  sparklyr::invoke("sql", 
                   "SELECT userid, CONCAT_WS(', ', collect_list(city)) AS cities
                   OVER (PARTITION BY userid
                         ORDER BY date)
                   FROM my_sdf") %>%
  sparklyr::sdf_register() %>%
  sparklyr::sdf_copy_to(sc, ., "my_sdf", overwrite = T)

^ 抛出以下错误：

Error: org.apache.spark.sql.catalyst.parser.ParseException: 
mismatched input 'OVER' expecting <EOF>(line 2, pos 19)

== SQL ==
SELECT userid, conversion_location, CONCAT_WS(' > ', collect_list(channel)) AS path
                   OVER (PARTITION BY userid, conversion_location
-------------------^^^
                         ORDER BY occurred_at)
                   FROM paths_model

Answer 1

解决了！我误解了 collect_list() 和 Spark SQL 如何协同工作。我没有意识到可以返回一个列表，我认为连接必须在查询中进行。以下产生了预期的结果：

spark_output <- spark_session(sc) %>%
  sparklyr::invoke("sql", 
                   "SELECT userid, collect_list(city)
                   OVER (PARTITION BY userid
                         ORDER BY date
                         ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING)
                   AS cities
                   FROM my_sdf") %>%
  sdf_register() %>%
  group_by(userid) %>%
  filter(row_number(userid) == 1) %>%
  ungroup() %>%
  mutate(cities = paste(cities, sep = " > ")) %>%
  sdf_register()

Answer 2

好的：所以我承认以下解决方案根本没有效率（它使用 for 循环，实际上是很多代码，看起来可能是一项简单的任务），但我相信这应该可行：

#install.packages("tidyverse") # if needed
library(tidyverse)

df <- tribble(
  ~userid, ~date, ~city,
  1   ,  "2018-08-02"  ,   "A",
  1   ,  "2018-08-03"  ,   "B",
  1   ,  "2018-08-04"  ,   "C",
  2   ,  "2018-08-17"  ,   "G",
  2   ,  "2018-08-20"  ,   "E",
  2   ,  "2018-08-23"  ,   "F"
)

cityPerId <- df %>% 
  spread(key = date, value = city) 

toMutate <- NA
for (i in 1:nrow(cityPerId)) {
  cities <- cityPerId[i,][2:ncol(cityPerId)] %>% t() %>%
    as.vector() %>% 
    na.omit()
  collapsedCities <- paste(cities, collapse = ",")
  toMutate <- c(toMutate, collapsedCities)
}
toMutate <- toMutate[2:length(toMutate)]

final <- cityPerId %>% 
  mutate(cities = toMutate) %>% 
  select(userid, cities)