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From James Marca <jma...@translab.its.uci.edu>
Subject wiki edit on built-in reduce functions
Date Wed, 18 Jan 2012 01:31:50 GMT
Hi, 

this is a quick note for whomever is in charge of the wiki (my wiki
account no longer has write ability)

Built-In_Reduce_Functions says that you need to emit numbers for the
_sum operation.  As of 1.2.x, this can also be a list of numbers.

I just emitted a list of numbers and got what I expected...that is, a
sum over each element of the list (not a summing up of the elements,
summed.

Example:

no reducing, I emit a list of 4 items for each key:

["2007-02-27", "1213122", "2007-02-27 14:46:00 UTC"]   [0.000007830687904038072, 0.000001032961291729275,0.0000012756780418961,
2.209310910297831e-7]
["2007-02-27", "1213122", "2007-02-27 14:46:30 UTC"]   [0.000008151766266816958, 0.000001042421330553939,0.000001315925015500657,
2.278253064474915e-7]

"Exact" reducing, same as emit with no reduce:

["2007-02-27", "1213122", "2007-02-27 14:46:00 UTC"]   [0.000007830687904038072, 0.000001032961291729275,0.0000012756780418961,
2.209310910297831e-7]
["2007-02-27", "1213122", "2007-02-27 14:46:30 UTC"]   [0.000008151766266816958, 0.000001042421330553939,0.000001315925015500657,
2.278253064474915e-7]

level=1 reducing, summing up over each day

["2007-02-27"]   [0.003547119931415267, 0.005496433891250249, 0.007064010452051014,0.003552803842322634]
["2007-02-28"]   [0.008437247339553495, 0.01664606221946668, 0.01779585111017863,0.01036210620457586]


I observed this behavior in 1.2.x. I know this hasn't always been a
feature, but I couldn't find whether it was 1.1 or 1.0, or what.

Regards, 
James Marca

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