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From André Pinto <andredasilvapi...@gmail.com>
Subject Re: Percentile rank
Date Mon, 06 Apr 2015 22:19:37 GMT
Hi Josh,

Thanks for replying.

That really sounds very hacky. I was expecting something with a little more
support from the API.

I guess we could also use sortAndApply with a random generated singleton
Key for the entire set of values and then use the Iterable on the Values to
obtain the sorted index. It still looks bad though...

Just out of curiosity, why isn't the Iterable approach also supported on
the simple Sort.sort? Sorry if this looks obvious to you, but I'm still new
to Crunch and Hadoop.

Thanks.

On Thu, Apr 2, 2015 at 6:36 PM, Josh Wills <jwills@cloudera.com> wrote:

> I can't think of a great way to do it-- knowing exactly which record
> you're processing (in any kind of order) in a distributed processing job is
> always somewhat fraught. Gun to my head, I would do it in two phases:
>
> 1) Get the name of the FileSplit for the current task-- which can be
> retrieved, although we don't make it easy. You can do it via something like
> this from inside of a map-side DoFn:
>
> InputSplit split = ((MapContext) getContext()).getInputSplit();
> FileSplit baseSplit = (FileSplit) ((Supplier<InputSplit>) split).get();
>
> The count up the number of records inside of each FileSplit. I'm not sure
> if you should disable combine files when you do this, but it seems like a
> good idea.
>
> 2) Create a new DoFn that takes the output of the previous job and uses it
> to determine exactly which record in order the currently processing record
> is, based on the sorted order of the FileSplit names and an internal
> counter that gets reset to zero for each new FileSplit.
>
> J
>
> On Thu, Apr 2, 2015 at 7:39 AM, André Pinto <andredasilvapinto@gmail.com>
> wrote:
>
>> Hi,
>>
>> I'm trying to calculate the percentile ranks for the values of a sorted
>> PTable (i.e. at which % rank each element is within the whole data set). Is
>> there a way to do this with Crunch? Seems that we would only need to have
>> access to the global index of the record during an iteration over the data
>> set.
>>
>> Thanks in advance,
>> André
>>
>>
>
>
> --
> Director of Data Science
> Cloudera <http://www.cloudera.com>
> Twitter: @josh_wills <http://twitter.com/josh_wills>
>

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