如何在星火数据帧中添加一个常数列? [英] How to add a constant column in a Spark DataFrame?
问题描述
我想在数据帧
与一些任意值(即每一行的相同)添加一列。当我使用我得到一个错误 withColumn
如下:
I want to add a column in a DataFrame
with some arbitrary value (that is the same for each row). I get an error when I use withColumn
as follows:
dt.withColumn('new_column', 10).head(5)
---------------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-50-a6d0257ca2be> in <module>()
1 dt = (messages
2 .select(messages.fromuserid, messages.messagetype, floor(messages.datetime/(1000*60*5)).alias("dt")))
----> 3 dt.withColumn('new_column', 10).head(5)
/Users/evanzamir/spark-1.4.1/python/pyspark/sql/dataframe.pyc in withColumn(self, colName, col)
1166 [Row(age=2, name=u'Alice', age2=4), Row(age=5, name=u'Bob', age2=7)]
1167 """
-> 1168 return self.select('*', col.alias(colName))
1169
1170 @ignore_unicode_prefix
AttributeError: 'int' object has no attribute 'alias'
看来我可以欺骗功能进入工作,因为我想通过添加和减去其他列中的一个(因此它们添加到零),然后(在这种情况下,10)将欲数:
It seems that I can trick the function into working as I want by adding and subtracting one of the other columns (so they add to zero) and then adding the number I want (10 in this case):
dt.withColumn('new_column', dt.messagetype - dt.messagetype + 10).head(5)
[Row(fromuserid=425, messagetype=1, dt=4809600.0, new_column=10),
Row(fromuserid=47019141, messagetype=1, dt=4809600.0, new_column=10),
Row(fromuserid=49746356, messagetype=1, dt=4809600.0, new_column=10),
Row(fromuserid=93506471, messagetype=1, dt=4809600.0, new_column=10),
Row(fromuserid=80488242, messagetype=1, dt=4809600.0, new_column=10)]
这是苏premely哈克,对不对?我认为还有一个更合法的方式做到这一点?
This is supremely hacky, right? I assume there is a more legit way to do this?
推荐答案
的 DataFrame.withColumn
第二个参数应该是一个列
,所以你必须使用文字:
The second argument for DataFrame.withColumn
should be a Column
so you have to use a literal:
from pyspark.sql.functions import lit
df.withColumn('new_column', lit(10))
如果您需要复杂的栏,你可以建立这些使用块如阵列
:
If you need complex columns you can build these using blocks like array
:
from pyspark.sql.functions import array, struct
df.withColumn("some_array", array(lit(1), lit(2), lit(3)))
df.withColumn("some_struct", struct(lit("foo"), lit(1), lit(.3)))
完全一样的方法可以在Scala中使用。
Exactly the same methods can be used in Scala.
import org.apache.spark.sql.functions.lit
df.withColumn('new_column', lit(10))
另外,也可以,虽然慢,要使用UDF
It is also possible, although slower, to use an UDF.
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