你如何使用Python执行两个RDD表基本联接在星火? [英] How do you perform basic joins of two RDD tables in Spark using Python?
问题描述
您将如何执行使用python Spark中的基本连接?在R您可以使用MERG()来做到这一点。什么是使用python的火花的语法:
How would you perform basic joins in Spark using python? In R you could use merg() to do this. What is the syntax using python on spark for:
- 内加入
- 左外连接
- 十字加入
使用两个表格(RDD)在每个单个列,有一个共同的密钥。
With two tables (RDD) with a single column in each that has a common key.
RDD(1):(key,U)
RDD(2):(key,V)
我觉得一个内部联接是这样的:
I think an inner join is something like this:
rdd1.join(rdd2).map(case (key, u, v) => (key, ls ++ rs));
是吗?我已经在网上搜索,找不到加入的一个很好的例子。先谢谢了。
Is that right? I have searched the internet and can't find a good example of joins. Thanks in advance.
推荐答案
可以使用PairRDDs要么做或Spark数据帧。由于数据帧从操作催化剂受益优化第二个选项可以值得考虑。
It can be done either using PairRDDs or Spark Data Frames. Since data frame operations benefit from Catalyst Optimizer the second option can worth considering.
假设你的数据看起来如下:
Assuming your data looks as follows:
rdd1 = sc.parallelize([("foo", 1), ("bar", 2), ("baz", 3)])
rdd2 = sc.parallelize([("foo", 4), ("bar", 5), ("bar", 6)])
随着PairRDDs:
内连接:
rdd1.join(rdd2)
LEFT OUTER JOIN:
Left outer join:
rdd1.leftOuterJoin(rdd2)
笛卡尔乘积:
rdd1.cartesian(rdd2)
广播加入:
- 请参见星火:什么是加盟一个2元组键RDD用单键RDD最好的策略 <? / LI>
- see Spark: what's the best strategy for joining a 2-tuple-key RDD with single-key RDD?
最后是协同组
有没有直接的SQL等价的,但在某些情况下是有用的:
Finally there is cogroup
which has no direct SQL equivalent but can be useful in some situations:
cogrouped = rdd1.cogroup(rdd2)
cogrouped.mapValues(lambda x: (list(x[0]), list(x[1]))).collect()
## [('foo', ([1], [4])), ('bar', ([2], [5, 6])), ('baz', ([3], []))]
火花数据帧
您可以使用SQL DSL或使用执行原始的SQL sqlContext.sql
。
df1 = sqlContext.createDataFrame(rdd1, ('k', 'v1'))
df2 = sqlContext.createDataFrame(rdd2, ('k', 'v2'))
# Register temporary tables to be able to use sqlContext.sql
df1.registerTempTable('df1')
df2.registerTempTable('df2')
内连接:
# inner is a default value so it could be omitted
df1.join(df2, df1.k == df2.k, joinType='inner')
sqlContext.sql('SELECT * FROM df1 JOIN df2 ON df1.k = df2.k')
LEFT OUTER JOIN:
Left outer join:
df1.join(df2, df1.k == df2.k, joinType='left_outer')
sqlContext.sql('SELECT * FROM df1 LEFT OUTER JOIN df2 ON df1.k = df2.k')
CROSS JOIN:
Cross join:
df1.join(df2)
sqlContext.sql('SELECT * FROM df1 JOIN df2')
由于1.6(1.5 Scala中)每个这些可以用广播相结合
功能:
from pyspark.sql.functions import broadcast
df1.join(broadcast(df2))
执行广播加盟。另请参见为什么我BroadcastHashJoin是星火比ShuffledHashJoin慢
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