如何将pyspark dataframe中单元格中的CSV值分别分离为新列及其值

Question

当前的spark数据帧在一列的单元格级别具有CSV值，我试图将其分解为新列。示例数据帧

    a_id                                    features
1   2020     "a","b","c","d","constant1","1","0.1","aa"
2   2021     "a","b","c","d","constant2","1","0.2","ab"
3   2022     "a","b","c","d","constant3","1","0.3","ac","a","b","c","d","constant3","1.1","3.3","acx"
4   2023     "a","b","c","d","constant4","1","0.4","ad"
5   2024     "a","b","c","d","constant5","1","0.5","ae","a","b","c","d","constant5","1.2","6.3","xwy","a","b","c","d","constant5","2.2","8.3","bunr"
6   2025     "a","b","c","d","constant6","1","0.6","af"

features列有多个csv值，其中（a、b、c、d）作为标题，它们在某些单元格（第3行和第5行）中重复，我只想提取一个标题及其相应的值。预期数据帧的输出如图所示

输出火花数据帧

    a_id       a        d
1   2020   constant1   ["aa"]
2   2021   constant2   ["ab"]
3   2022   constant3   ["ac","acx"]
4   2023   constant4   ["ad"]
5   2024   constant5   ["ae","xwy","bunr"]
6   2025   constant6   ["af"]

如图所示，我只想将a和d标题提取为新列，其中a是常量，d有多个值，其中其值作为列表

请帮助如何在pysaprk中转换此文件。上述数据帧是实时流式数据帧

Answer 1

仅使用Pyspark/Spark SQL函数：

• 从字符串中删除标题
• 使用regexp_extract_all提取子字符串，在每四个,之后将字符串分成子字符串
• explode返回结果并删除空行
• split再次显示结果。现在，每个csv值都是数组的一个元素
• 从数组的第一个和第四个元素创建列a和d
• 分组依据a_id

from pyspark.sql import functions as F

header='"a","b","c","d",'
num_headers = header.count(",")

df.withColumn("features", F.expr(f"replace(features, '{header}')")) \
  .withColumn("features", F.expr(f"regexp_extract_all(features, '(([^,]*,?)\\{{{num_headers}}})')")) \
  .withColumn("features", F.explode("features"))\
  .filter("not features =''") \
  .withColumn("features", F.split("features", ",")) \
  .withColumn("a", F.expr("features[0]")) \
  .withColumn("d", F.expr("features[3]")) \
  .groupBy("a_id") \
  .agg(F.first("a").alias("a"), F.collect_list("d").alias("d")) \
  .show(truncate=False)

输出：

+  +     +          -+
|a_id|a         |d                    |
+  +     +          -+
|2020|"constant"|["aa"]               |
|2022|"constant"|["ac", "acx"]        |
|2025|"constant"|["af"]               |
|2023|"constant"|["ad"]               |
|2021|"constant"|["ab"]               |
|2024|"constant"|["ae", "xwy", "bunr"]|
+  +     +          -+