多列上的 Groupby 和枢轴 PySpark 数据框

Question

我是 Spark 的新手，想在多个列上旋转 PySpark 数据框。每个不同的（日期、等级）组合都有一行。这些行应该被展平，以便每个唯一日期有一行。

import pyspark.sql.functions as F
from datetime import datetime

data= [(datetime(2021,8,4,13,0), 1, 22, "a"),(datetime(2021,8,4,13,0), 2, 14, "a"),(datetime(2021,8,4,13,0), 3, 9, "a"),(datetime(2021,8,4,13,0), 4, 7, "a"),
       (datetime(2021,8,4,14,0), 1, 16, "b"),(datetime(2021,8,4,14,0), 2, 21, "b"),(datetime(2021,8,4,14,0), 3, 17, "b"),(datetime(2021,8,4,14,0), 4, 18, "b"),
       (datetime(2021,8,4,15,0), 1, 19, "a"),(datetime(2021,8,4,15,0), 2, 9, "b"),(datetime(2021,8,4,15,0), 3, 10, "c"),(datetime(2021,8,4,15,0), 4, 13, "d")
      ]
        
columns= ["date","rank","feat1","feat2"]
df = spark.createDataFrame(data = data, schema = columns)
df.show(truncate=False)

+-------------------+----+-----+-----+
|date               |rank|feat1|feat2|
+-------------------+----+-----+-----+
|2021-08-04 13:00:00|1   |22   |a    |
|2021-08-04 13:00:00|2   |14   |a    |
|2021-08-04 13:00:00|3   |9    |a    |
|2021-08-04 13:00:00|4   |7    |a    |
|2021-08-04 14:00:00|1   |16   |b    |
|2021-08-04 14:00:00|2   |21   |b    |
|2021-08-04 14:00:00|3   |17   |b    |
|2021-08-04 14:00:00|4   |18   |b    |
|2021-08-04 15:00:00|1   |19   |a    |
|2021-08-04 15:00:00|2   |9    |b    |
|2021-08-04 15:00:00|3   |10   |c    |
|2021-08-04 15:00:00|4   |13   |d    |
+-------------------+----+-----+-----+

真实数据有 30+ 个特征列，每个日期的排名从 1 到 100。所需的输出：

+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
|               date|rank1_feat1|rank2_feat1|rank3_feat1|rank4_feat1|rank1_feat2|rank2_feat2|rank3_feat2|rank4_feat2|
+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
|2021-08-04 15:00:00|         19|          9|         10|         13|          a|          b|          c|          d|
|2021-08-04 13:00:00|         22|         14|          9|          7|          a|          a|          a|          a|
|2021-08-04 14:00:00|         16|         21|         17|         18|          b|          b|          b|          b|
+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+

我有一个似乎适用于我的简单示例的解决方案，但内存使用量非常大，以至于我什至无法使用 1/500 的数据而不会出现内存错误。

dfspine = df.select("date").distinct()

for col in df.columns:
    if col not in ["date", "rank"]:
        piv = df.groupby("date").pivot("rank").agg(F.first(col))
        mapping = dict([(pivcol,"rank%s_%s" % (pivcol, col)) for pivcol in piv.columns if pivcol not in ["date"]])
        piv = piv.select([F.col(c).alias(mapping.get(c, c)) for c in piv.columns])
        dfspine = dfspine.join(piv, how="left", on="date")

Answer 1

在 pandas 中这是相当微不足道的。这是一个融化和支点。在 pyspark 中，由于缺乏融化，它有点困难。幸运的是 this post 有一个在 pyspark 中重新创建熔体的解决方案。我们可以以此为基础。

熊猫版：

import pandas as pd
pdf = pd.DataFrame({'date': ['2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00'],
 'rank': [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4],
 'feat1': [22, 14, 9, 7, 16, 21, 17, 18, 19, 9, 10, 13],
 'feat2': ['a', 'a', 'a', 'a', 'b', 'b', 'b', 'b', 'a', 'b', 'c', 'd']})

pdf = pdf.melt(id_vars=['date', 'rank'])
pdf['col'] = 'rank' + pdf['rank'].astype(str) + '_' + pdf['variable']
pdf.pivot(index='date',columns='col',values='value')

pyspark 版本：

import pandas as pd
from pyspark.sql.functions import array, col, explode, lit, struct, concat, first
from pyspark.sql import DataFrame
from typing import Iterable 

def melt(
        df: DataFrame, 
        id_vars: Iterable[str], value_vars: Iterable[str], 
        var_name: str="variable", value_name: str="value") -> DataFrame:
    """Convert :class:`DataFrame` from wide to long format."""

    # Create array<struct<variable: str, value: ...>>
    _vars_and_vals = array(*(
        struct(lit(c).alias(var_name), col(c).alias(value_name)) 
        for c in value_vars))

    # Add to the DataFrame and explode
    _tmp = df.withColumn("_vars_and_vals", explode(_vars_and_vals))

    cols = id_vars + [
            col("_vars_and_vals")[x].alias(x) for x in [var_name, value_name]]
    return _tmp.select(*cols)

pdf = pd.DataFrame({'date': ['2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 13:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 14:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00',
  '2021-08-04 15:00:00'],
 'rank': [1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4],
 'feat1': [22, 14, 9, 7, 16, 21, 17, 18, 19, 9, 10, 13],
 'feat2': ['a', 'a', 'a', 'a', 'b', 'b', 'b', 'b', 'a', 'b', 'c', 'd']})

sdf = spark.createDataFrame(pdf)
sdf = melt(sdf, id_vars=['date', 'rank'], value_vars=['feat1','feat2'])
sdf = sdf.withColumn('rank', concat(lit('rank'),col('rank'), lit('_'),col('variable')))
sdf = sdf.groupby('date').pivot('rank').agg(first(col('value')))

输出

+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
|               date|rank1_feat1|rank1_feat2|rank2_feat1|rank2_feat2|rank3_feat1|rank3_feat2|rank4_feat1|rank4_feat2|
+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+
|2021-08-04 13:00:00|         22|          a|         14|          a|          9|          a|          7|          a|
|2021-08-04 14:00:00|         16|          b|         21|          b|         17|          b|         18|          b|
|2021-08-04 15:00:00|         19|          a|          9|          b|         10|          c|         13|          d|
+-------------------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+-----------+