Spark: Convert column of string to an array

问题

How to convert a column that has been read as a string into a column of arrays? i.e. convert from below schema

scala> test.printSchema
root
 |-- a: long (nullable = true)
 |-- b: string (nullable = true)

+---+---+
|  a|  b|
+---+---+
|  1|2,3|
+---+---+
|  2|4,5|
+---+---+

To:

scala> test1.printSchema
root
 |-- a: long (nullable = true)
 |-- b: array (nullable = true)
 |    |-- element: long (containsNull = true)

+---+-----+
|  a|  b  |
+---+-----+
|  1|[2,3]|
+---+-----+
|  2|[4,5]|
+---+-----+

Please share both scala and python implementation if possible. On a related note, how do I take care of it while reading from the file itself? I have data with ~450 columns and few of them I want to specify in this format. Currently I am reading in pyspark as below:

df = spark.read.format('com.databricks.spark.csv').options(
    header='true', inferschema='true', delimiter='|').load(input_file)

Thanks.

回答1:

There are various method,

The best way to do is using split function and cast to array<long>

data.withColumn("b", split(col("b"), ",").cast("array<long>"))

You can also create simple udf to convert the values

val tolong = udf((value : String) => value.split(",").map(_.toLong))

data.withColumn("newB", tolong(data("b"))).show

Hope this helps!

回答2:

Using a UDF would give you exact required schema. Like this:

val toArray = udf((b: String) => b.split(",").map(_.toLong))

val test1 = test.withColumn("b", toArray(col("b")))

It would give you schema as follows:

scala> test1.printSchema
root
 |-- a: long (nullable = true)
 |-- b: array (nullable = true)
 |    |-- element: long (containsNull = true)

+---+-----+
|  a|  b  |
+---+-----+
|  1|[2,3]|
+---+-----+
|  2|[4,5]|
+---+-----+

As far as applying schema on file read itself is concerned, I think that is a tough task. So, for now you can apply transformation after creating DataFrameReader of test.

I hope this helps!

回答3:

In python (pyspark) it would be:

from pyspark.sql.types import *
from pyspark.sql.functions import col, split
test = test.withColumn(
        "b",
        split(col("b"), ",\s*").cast("array<int>").alias("ev")
 )

来源：https://stackoverflow.com/questions/44690174/spark-convert-column-of-string-to-an-array

标签

scala

apache-spark

pyspark