pyspark:从现有列创建MapType列 [英] pyspark: Create MapType Column from existing columns
问题描述
我需要基于现有的列创建一个新的Spark DF MapType列,其中列名是键,值是值.
I need to creeate an new Spark DF MapType Column based on the existing columns where column name is the key and the value is the value.
例如-我有这个DF:
rdd = sc.parallelize([('123k', 1.3, 6.3, 7.6),
('d23d', 1.5, 2.0, 2.2),
('as3d', 2.2, 4.3, 9.0)
])
schema = StructType([StructField('key', StringType(), True),
StructField('metric1', FloatType(), True),
StructField('metric2', FloatType(), True),
StructField('metric3', FloatType(), True)])
df = sqlContext.createDataFrame(rdd, schema)
+----+-------+-------+-------+
| key|metric1|metric2|metric3|
+----+-------+-------+-------+
|123k| 1.3| 6.3| 7.6|
|d23d| 1.5| 2.0| 2.2|
|as3d| 2.2| 4.3| 9.0|
+----+-------+-------+-------+
到目前为止,我已经可以从中创建一个structType了:
I'm already so far that i can create a structType from this:
nameCol = struct([name for name in df.columns if ("metric" in name)]).alias("metric")
df2 = df.select("key", nameCol)
+----+-------------+
| key| metric|
+----+-------------+
|123k|[1.3,6.3,7.6]|
|d23d|[1.5,2.0,2.2]|
|as3d|[2.2,4.3,9.0]|
+----+-------------+
但是我需要的是一个具有am MapType的度量标准列,其中键是列名:
But what i need is an metric column with am MapType where the key is the column name:
+----+-------------------------+
| key| metric|
+----+-------------------------+
|123k|Map(metric1 -> 1.3, me...|
|d23d|Map(metric1 -> 1.5, me...|
|as3d|Map(metric1 -> 2.2, me...|
+----+-------------------------+
有没有提示我如何转换数据?
Any hints how i can transform the data?
谢谢!
推荐答案
在Spark 2.0或更高版本中,您可以使用create_map
.首先是一些进口:
In Spark 2.0 or later you can use create_map
. First some imports:
from pyspark.sql.functions import lit, col, create_map
from itertools import chain
create_map
期望keys
和values
的交错序列,可以像这样创建:
create_map
expects an interleaved sequence of keys
and values
which can be created for example like this:
metric = create_map(list(chain(*(
(lit(name), col(name)) for name in df.columns if "metric" in name
)))).alias("metric")
并与select
一起使用:
df.select("key", metric)
使用示例数据,结果为:
With example data the result is:
+----+---------------------------------------------------------+
|key |metric |
+----+---------------------------------------------------------+
|123k|Map(metric1 -> 1.3, metric2 -> 6.3, metric3 -> 7.6) |
|d23d|Map(metric1 -> 1.5, metric2 -> 2.0, metric3 -> 2.2) |
|as3d|Map(metric1 -> 2.2, metric2 -> 4.3, metric3 -> 9.0) |
+----+---------------------------------------------------------+
如果使用早期版本的Spark,则必须使用UDF:
If you use an earlier version of Spark you'll have to use UDF:
from pyspark.sql import Column
from pyspark.sql.functions import struct
from pyspark.sql.types import DataType, DoubleType, StringType, MapType
def as_map(*cols: str, key_type: DataType=DoubleType()) -> Column:
args = [struct(lit(name), col(name)) for name in cols]
as_map_ = udf(
lambda *args: dict(args),
MapType(StringType(), key_type)
)
return as_map_(*args)
可以如下使用:
df.select("key",
as_map(*[name for name in df.columns if "metric" in name]).alias("metric"))
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