On 9/12/12 11:12 PM, Cheolsoo Park wrote:
I am puzzled about this. If I am not mistaken, the SAMPLE operator is
nothing but "Math.random() < x" where "x" is a double.
You are right. Sample operator translates in to a filter operator with
condition "Math.random() < x".
In my test, SAMPLE A 0.00001 returns about 10 records with a million
records when running in local mode. I am curious if something can go wrong
when running it in MR mode.
I wouldn't expect different behavior in case of MR mode.
Brian,
Do you see this behavior across multiple runs ?
-Thejas
On Tue, Sep 11, 2012 at 3:37 PM, Brian Choi <[email protected]> wrote:
Hello Everyone,
I am wondering if anyone has run into an issue that I am having
using SAMPLE in a pig script to create a subsample of 0.001% from the
orignal relation.
Assume the relation "A" contains a single column of data (int type) with
1,000,000 records
Asamp = SAMPLE A 0.00001;
Asamp2 = SAMPLE A 0.0001;
Asamp and Asamp2 should produce subsampled relations with 10 and 100
records, respectively. However, what I find is Asamp and Asamp2 are closer
to 1000 and 10000 records, which seems like a 100-fold error in sample
size. Interestingly, in the limiting case of:
Asamp3 = SAMPLE A 0.99;
The actual subsampled size is VERY close to the expected 99% size of the
full sample size. Can anyone shed light as to what I may be doing wrong or
share their experiences if they have also seen issues with using SAMPLE in
PIG. Thank you.
Brian
