使用Spark将列转置为行 [英] Transpose column to row with Spark

问题描述

我正在尝试将表的某些列转置为行. 我正在使用Python和Spark 1.5.0.这是我的初始表格:

I'm trying to transpose some columns of my table to row. I'm using Python and Spark 1.5.0. Here is my initial table:

+-----+-----+-----+-------+
|  A  |col_1|col_2|col_...|
+-----+-------------------+
|  1  |  0.0|  0.6|  ...  |
|  2  |  0.6|  0.7|  ...  |
|  3  |  0.5|  0.9|  ...  |
|  ...|  ...|  ...|  ...  |

我想吃点这样的东西

+-----+--------+-----------+
|  A  | col_id | col_value |
+-----+--------+-----------+
|  1  |   col_1|        0.0|
|  1  |   col_2|        0.6|   
|  ...|     ...|        ...|    
|  2  |   col_1|        0.6|
|  2  |   col_2|        0.7| 
|  ...|     ...|        ...|  
|  3  |   col_1|        0.5|
|  3  |   col_2|        0.9|
|  ...|     ...|        ...|

有人知道我能做到吗?谢谢您的帮助.

Does someone know haw I can do it? Thank you for your help.

推荐答案

使用基本的Spark SQL函数相对简单.

It is relatively simple to do with basic Spark SQL functions.

Python

from pyspark.sql.functions import array, col, explode, struct, lit

df = sc.parallelize([(1, 0.0, 0.6), (1, 0.6, 0.7)]).toDF(["A", "col_1", "col_2"])

def to_long(df, by):

    # Filter dtypes and split into column names and type description
    cols, dtypes = zip(*((c, t) for (c, t) in df.dtypes if c not in by))
    # Spark SQL supports only homogeneous columns
    assert len(set(dtypes)) == 1, "All columns have to be of the same type"

    # Create and explode an array of (column_name, column_value) structs
    kvs = explode(array([
      struct(lit(c).alias("key"), col(c).alias("val")) for c in cols
    ])).alias("kvs")

    return df.select(by + [kvs]).select(by + ["kvs.key", "kvs.val"])

to_long(df, ["A"])

斯卡拉:

import org.apache.spark.sql.DataFrame
import org.apache.spark.sql.functions.{array, col, explode, lit, struct}

val df = Seq((1, 0.0, 0.6), (1, 0.6, 0.7)).toDF("A", "col_1", "col_2")

def toLong(df: DataFrame, by: Seq[String]): DataFrame = {
  val (cols, types) = df.dtypes.filter{ case (c, _) => !by.contains(c)}.unzip
  require(types.distinct.size == 1, s"${types.distinct.toString}.length != 1")      

  val kvs = explode(array(
    cols.map(c => struct(lit(c).alias("key"), col(c).alias("val"))): _*
  ))

  val byExprs = by.map(col(_))

  df
    .select(byExprs :+ kvs.alias("_kvs"): _*)
    .select(byExprs ++ Seq($"_kvs.key", $"_kvs.val"): _*)
}

toLong(df, Seq("A"))

这篇关于使用Spark将列转置为行的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！