Just to clarify: .99 does NOT work fine. It should have rejected most of the
records when I specified "((Math.random())>=.99)".
I have used expressions not involving Math.random. For example, I can extract
records above a specific score with "score>1.0". But the random thing doesn't
work even though I have tried various thresholds.
On Tuesday, May 1, 2018, 2:00:48 PM PDT, Markus Jelsma
<[email protected]> wrote:
Hello Michael,
I would think this should work as well. But since you mention .99 works fine,
did you try .1 as well to get ~10% output? It seems the expressions itself do
work at some level, and since this is a Jexl specific thing, you might want to
try the Jexl list as well. I could not find an online Jexl parser to test this
question, it would be really helpful!
Regards,
Markus
-----Original message-----
> From:Michael Coffey <[email protected]>
> Sent: Tuesday 1st May 2018 22:47
> To: User <[email protected]>
> Subject: random sampling of crawlDb urls
>
> I want to extract a random sample of URLS from my big crawldb. I think I
> should be able to do this using readdb -dump with a Jexl expression, but I
> haven't been able to get it to work.
>
> I have tried several variations of the following command.
> $NUTCH_HOME/runtime/deploy/bin/nutch readdb /crawls/pop2/data/crawldb -dump
> /crawls/pop2/data/crawldb/pruned/current -format crawldb -expr
> "((Math.random())>=0.1)"
>
>
> Typically, it produces zero records. I know the expression is getting through
> to the CrawlDbReader (without quotes) because I get this message:
> 18/05/01 13:22:48 INFO crawl.CrawlDbReader: CrawlDb db: expr:
> ((Math.random())>=0.1)
>
> Even when I use the expression "((Math.random())>=0.0)" I get zero output
> records.
>
> If I use the expression "((Math.random())>=.99)" it lets all records pass
> through to the output. I guess it has something to do with the lack of
> leading zero on the numeric constant.
>
> Does anyone know a good way to extract a random sample of records from a
> crawlDb?
>
