如何使用 Sparklyr 包将不同数据类型的数据展平？

Question

简介

R 代码是使用 Sparklyr 包编写的，用于创建数据库模式。 [给出了可重现的代码和数据库]

现有结果

root
|-- contributors : string
|-- created_at : string
|-- entities (struct)
|     |-- hashtags (array) : [string]
|     |-- media (array)
|     |     |-- additional_media_info (struct)
|     |     |       |-- description : string
|     |     |       |-- embeddable : boolean
|     |     |       |-- monetizable : bollean
|     |     |-- diplay_url : string
|     |     |-- id : long
|     |     |-- id_str : string
|     |-- urls (array)     
|-- extended_entities (struct)
|-- retweeted_status (struct)
|-- user (struct)

我想将这个结构展平如下，

预期结果

root
|-- contributors : string
|-- created_at : string
|-- entities (struct)
|-- entities.hashtags (array) : [string]
|-- entities.media (array)
|-- entities.media.additional_media_info (struct)
|-- entities.media.additional_media_info.description : string
|-- entities.media.additional_media_info.embeddable : boolean
|-- entities.media.additional_media_info.monetizable : bollean
|-- entities.media.diplay_url : string
|-- entities.media.id : long
|-- entities.media.id_str : string
|-- entities.urls (array)     
|-- extended_entities (struct)
|-- retweeted_status (struct)
|-- user (struct)

数据库 导航至： Data-178 KB。然后将编号的项目复制到名为 "example" 的文本文件中。保存到在您的工作目录中创建的名为“../example.json/”的目录。

编写 R 代码以重现如下示例，

退出代码

library(sparklyr)
library(dplyr)
library(devtools)
  devtools::install_github("mitre/sparklyr.nested")
# If Spark is not installed, then also need:
# spark_install(version = "2.2.0")
library(sparklyr.nested)
library(testthat)
library(jsonlite)

Sys.setenv(SPARK_HOME="/usr/lib/spark")    
conf <- spark_config()
conf$'sparklyr.shell.executor-memory' <- "20g"
conf$'sparklyr.shell.driver-memory' <- "20g"
conf$spark.executor.cores <- 16
conf$spark.executor.memory <- "20G"
conf$spark.yarn.am.cores  <- 16
conf$spark.yarn.am.memory <- "20G"
conf$spark.executor.instances <- 8
conf$spark.dynamicAllocation.enabled <- "false"
conf$maximizeResourceAllocation <- "true"
conf$spark.default.parallelism <- 32
sc <- spark_connect(master = "local", config = conf, version = '2.2.0') # Connection             
 sample_tbl <- spark_read_json(sc,name="example",path="example.json", header = TRUE, memory = FALSE, overwrite = TRUE) 
 sdf_schema_viewer(sample_tbl) # to create db schema

付出的努力

使用 jsonlite。但它也无法读取大文件和块内的文件。花了很多时间。所以，我转向了 Sparklyr，因为它确实想知道并在几秒钟内读取了 10 亿条记录。我进一步研究了将记录展平到深层嵌套级别（因为展平是通过使用 flatten() 函数在 jsonlite 包中完成的）。但是，在 Sparklyr 中，没有这样的功能可用。在 Sparklyr 中，只有一级扁平化是可能的。

我想对不同数据类型的数据进行扁平化处理，并希望输出到CSV文件中。

Answer 1

好的，这是取消嵌套的一种可能方法。

您可以使用架构信息来创建所有嵌套名称。比如entities.media.additional_media_info，那么你就可以用SQL来select了。

这有点费力，可能无法一概而论，但有效

我认为这也应该很快，因为它只是一个 SELECT 语句。

columns_to_flatten <- sdf_schema_json(sample_tbl, simplify = T) %>%
  # using rlist package for ease of use
  rlist::list.flatten(use.names = T) %>%
  # get names
  names() %>%
  # remove contents of brackets and whitespace
  gsub("\(.*?\)|\s", "", .) %>%
  # add alias for column names, dot replaced with double underscore
  # this avoids duplicate names that would otherwise occur with singular
  {paste(., "AS", gsub("\.", "__", .))} %>%
  # required, otherwise doesn't seem to work
  sub("variants", "variants[0]", .)

# construct query
sql_statement <- paste("SELECT",
                       paste(columns_to_flatten, collapse = ", "),
                       "FROM example")

# execute on spark cluster, save as table in cluster
spark_session(sc) %>%
  sparklyr::invoke("sql", sql_statement) %>%
  sparklyr::invoke("createOrReplaceTempView", "flattened_example")

tbl(sc, "flattened_example") %>%
  sdf_schema_viewer()

生成的SQL是这样的，比较简单，就是长：

SELECT contributors AS contributors, coordinates AS coordinates, created_at AS created_at, display_text_range AS display_text_range, entities.hashtags.indices AS entities__hashtags__indices, entities.hashtags.text AS entities__hashtags__text, entities.media.additional_media_info.description AS entities__media__additional_media_info__description, entities.media.additional_media_info.embeddable AS entities__media__additional_media_info__embeddable, entities.media.additional_media_info.monetizable AS entities__media__additional_media_info__monetizable, entities.media.additional_media_info.title AS entities__media__additional_media_info__title, entities.media.display_url AS entities__media__display_url, entities.media.expanded_url AS entities__media__expanded_url, entities.media.id AS entities__media__id, entities.media.id_str AS entities__media__id_str, entities.media.indices AS entities__media__indices, entities.media.media_url AS entities__media__media_url, entities.media.media_url_https AS entities__media__media_url_https, entities.media.sizes.large.h AS entities__media__sizes__large__h, entities.media.sizes.large.resize AS entities__media__sizes__large__resize, entities.media.sizes.large.w AS entities__media__sizes__large__w FROM example

如何使用 Sparklyr 包将不同数据类型的数据展平？

How to flatten the data of different data types by using Sparklyr package?

r

apache-spark

nested

flatten

sparklyr