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From Pedro Rodriguez <ski.rodrig...@gmail.com>
Subject Re: Dataset Select Function after Aggregate Error
Date Sat, 18 Jun 2016 15:29:19 GMT
I am curious if there is a way to call this so that it becomes a compile
error rather than runtime error:

// Note mispelled count and name
ds.groupBy($"name").count.select('nam, $"coun").show

More specifically, what are the best type safety guarantees that Datasets
provide? It seems like with Dataframes there is still the unsafety of
specifying column names by string/symbol and expecting the type to be
correct and exist, but if you do something like this then downstream code
is safer:

// This is Array[(String, Long)] instead of Array[sql.Row]
ds.groupBy($"name").count.select('name.as[String], 'count.as
[Long]).collect()

Does that seem like a correct understanding of Datasets?

On Sat, Jun 18, 2016 at 6:39 AM, Pedro Rodriguez <ski.rodriguez@gmail.com>
wrote:

> Looks like it was my own fault. I had spark 2.0 cloned/built, but had the
> spark shell in my path so somehow 1.6.1 was being used instead of 2.0.
> Thanks
>
> On Sat, Jun 18, 2016 at 1:16 AM, Takeshi Yamamuro <linguin.m.s@gmail.com>
> wrote:
>
>> which version you use?
>> I passed in 2.0-preview as follows;
>> ---
>>
>> Spark context available as 'sc' (master = local[*], app id =
>> local-1466234043659).
>>
>> Spark session available as 'spark'.
>>
>> Welcome to
>>
>>       ____              __
>>
>>      / __/__  ___ _____/ /__
>>
>>     _\ \/ _ \/ _ `/ __/  '_/
>>
>>    /___/ .__/\_,_/_/ /_/\_\   version 2.0.0-preview
>>
>>       /_/
>>
>>
>>
>> Using Scala version 2.11.8 (Java HotSpot(TM) 64-Bit Server VM, Java
>> 1.8.0_31)
>>
>> Type in expressions to have them evaluated.
>>
>> Type :help for more information.
>>
>>
>> scala> val ds = Seq[Tuple2[Int, Int]]((1, 0), (2, 0)).toDS
>>
>> hive.metastore.schema.verification is not enabled so recording the schema
>> version 1.2.0
>>
>> ds: org.apache.spark.sql.Dataset[(Int, Int)] = [_1: int, _2: int]
>>
>> scala> ds.groupBy($"_1").count.select($"_1", $"count").show
>>
>> +---+-----+
>>
>> | _1|count|
>>
>> +---+-----+
>>
>> |  1|    1|
>>
>> |  2|    1|
>>
>> +---+-----+
>>
>>
>>
>> On Sat, Jun 18, 2016 at 3:09 PM, Pedro Rodriguez <ski.rodriguez@gmail.com
>> > wrote:
>>
>>> I went ahead and downloaded/compiled Spark 2.0 to try your code snippet
>>> Takeshi. It unfortunately doesn't compile.
>>>
>>> scala> val ds = Seq[Tuple2[Int, Int]]((1, 0), (2, 0)).toDS
>>> ds: org.apache.spark.sql.Dataset[(Int, Int)] = [_1: int, _2: int]
>>>
>>> scala> ds.groupBy($"_1").count.select($"_1", $"count").show
>>> <console>:28: error: type mismatch;
>>>  found   : org.apache.spark.sql.ColumnName
>>>  required: org.apache.spark.sql.TypedColumn[(org.apache.spark.sql.Row,
>>> Long),?]
>>>               ds.groupBy($"_1").count.select($"_1", $"count").show
>>>                                                                  ^
>>>
>>> I also gave a try to Xinh's suggestion using the code snippet below
>>> (partially from spark docs)
>>> scala> val ds = Seq(Person("Andy", 32), Person("Andy", 2),
>>> Person("Pedro", 24), Person("Bob", 42)).toDS()
>>> scala> ds.groupBy(_.name).count.select($"name".as[String]).show
>>> org.apache.spark.sql.AnalysisException: cannot resolve 'name' given
>>> input columns: [];
>>> scala> ds.groupBy(_.name).count.select($"_1".as[String]).show
>>> org.apache.spark.sql.AnalysisException: cannot resolve 'name' given
>>> input columns: [];
>>> scala> ds.groupBy($"name").count.select($"_1".as[String]).show
>>> org.apache.spark.sql.AnalysisException: cannot resolve '_1' given input
>>> columns: [];
>>>
>>> Looks like there are empty columns for some reason, the code below works
>>> fine for the simple aggregate
>>> scala> ds.groupBy(_.name).count.show
>>>
>>> Would be great to see an idiomatic example of using aggregates like
>>> these mixed with spark.sql.functions.
>>>
>>> Pedro
>>>
>>> On Fri, Jun 17, 2016 at 9:59 PM, Pedro Rodriguez <
>>> ski.rodriguez@gmail.com> wrote:
>>>
>>>> Thanks Xinh and Takeshi,
>>>>
>>>> I am trying to avoid map since my impression is that this uses a Scala
>>>> closure so is not optimized as well as doing column-wise operations is.
>>>>
>>>> Looks like the $ notation is the way to go, thanks for the help. Is
>>>> there an explanation of how this works? I imagine it is a method/function
>>>> with its name defined as $ in Scala?
>>>>
>>>> Lastly, are there prelim Spark 2.0 docs? If there isn't a good
>>>> description/guide of using this syntax I would be willing to contribute
>>>> some documentation.
>>>>
>>>> Pedro
>>>>
>>>> On Fri, Jun 17, 2016 at 8:53 PM, Takeshi Yamamuro <
>>>> linguin.m.s@gmail.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> In 2.0, you can say;
>>>>> val ds = Seq[Tuple2[Int, Int]]((1, 0), (2, 0)).toDS
>>>>> ds.groupBy($"_1").count.select($"_1", $"count").show
>>>>>
>>>>>
>>>>> // maropu
>>>>>
>>>>>
>>>>> On Sat, Jun 18, 2016 at 7:53 AM, Xinh Huynh <xinh.huynh@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Hi Pedro,
>>>>>>
>>>>>> In 1.6.1, you can do:
>>>>>> >> ds.groupBy(_.uid).count().map(_._1)
>>>>>> or
>>>>>> >> ds.groupBy(_.uid).count().select($"value".as[String])
>>>>>>
>>>>>> It doesn't have the exact same syntax as for DataFrame.
>>>>>> http://spark.apache.org/docs/latest/api/scala/index.html#org.apache.spark.sql.Dataset
>>>>>>
>>>>>> It might be different in 2.0.
>>>>>>
>>>>>> Xinh
>>>>>>
>>>>>> On Fri, Jun 17, 2016 at 3:33 PM, Pedro Rodriguez <
>>>>>> ski.rodriguez@gmail.com> wrote:
>>>>>>
>>>>>>> Hi All,
>>>>>>>
>>>>>>> I am working on using Datasets in 1.6.1 and eventually 2.0 when
its
>>>>>>> released.
>>>>>>>
>>>>>>> I am running the aggregate code below where I have a dataset
where
>>>>>>> the row has a field uid:
>>>>>>>
>>>>>>> ds.groupBy(_.uid).count()
>>>>>>> // res0: org.apache.spark.sql.Dataset[(String, Long)] = [_1:
>>>>>>> string, _2: bigint]
>>>>>>>
>>>>>>> This works as expected, however, attempts to run select statements
>>>>>>> after fails:
>>>>>>> ds.groupBy(_.uid).count().select(_._1)
>>>>>>> // error: missing parameter type for expanded function ((x$2)
=>
>>>>>>> x$2._1)
>>>>>>> ds.groupBy(_.uid).count().select(_._1)
>>>>>>>
>>>>>>> I have tried several variants, but nothing seems to work. Below
is
>>>>>>> the equivalent Dataframe code which works as expected:
>>>>>>> df.groupBy("uid").count().select("uid")
>>>>>>>
>>>>>>> Thanks!
>>>>>>> --
>>>>>>> Pedro Rodriguez
>>>>>>> PhD Student in Distributed Machine Learning | CU Boulder
>>>>>>> UC Berkeley AMPLab Alumni
>>>>>>>
>>>>>>> ski.rodriguez@gmail.com | pedrorodriguez.io | 909-353-4423
>>>>>>> Github: github.com/EntilZha | LinkedIn:
>>>>>>> https://www.linkedin.com/in/pedrorodriguezscience
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> ---
>>>>> Takeshi Yamamuro
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Pedro Rodriguez
>>>> PhD Student in Distributed Machine Learning | CU Boulder
>>>> UC Berkeley AMPLab Alumni
>>>>
>>>> ski.rodriguez@gmail.com | pedrorodriguez.io | 909-353-4423
>>>> Github: github.com/EntilZha | LinkedIn:
>>>> https://www.linkedin.com/in/pedrorodriguezscience
>>>>
>>>>
>>>
>>>
>>> --
>>> Pedro Rodriguez
>>> PhD Student in Distributed Machine Learning | CU Boulder
>>> UC Berkeley AMPLab Alumni
>>>
>>> ski.rodriguez@gmail.com | pedrorodriguez.io | 909-353-4423
>>> Github: github.com/EntilZha | LinkedIn:
>>> https://www.linkedin.com/in/pedrorodriguezscience
>>>
>>>
>>
>>
>> --
>> ---
>> Takeshi Yamamuro
>>
>
>
>
> --
> Pedro Rodriguez
> PhD Student in Distributed Machine Learning | CU Boulder
> UC Berkeley AMPLab Alumni
>
> ski.rodriguez@gmail.com | pedrorodriguez.io | 909-353-4423
> Github: github.com/EntilZha | LinkedIn:
> https://www.linkedin.com/in/pedrorodriguezscience
>
>


-- 
Pedro Rodriguez
PhD Student in Distributed Machine Learning | CU Boulder
UC Berkeley AMPLab Alumni

ski.rodriguez@gmail.com | pedrorodriguez.io | 909-353-4423
Github: github.com/EntilZha | LinkedIn:
https://www.linkedin.com/in/pedrorodriguezscience

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