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question regarding totals

Samuel Chen
Posted 13 years ago
Hi there,
I'd like to find out the total amount when the dates are the same. What is the best method when the data set has 3000 - 4000 rows?
{{{1, 1, 2000}, 2}, {{1, 2, 2000}, 1}, {{1, 2, 2000}, .2}}
Please help. Thanks.
Sam 
POSTED BY: Samuel Chen
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Nick Gaskill
Nick Gaskill
Posted 13 years ago
There's also a useful how-to in Documentation that talks about this...

How to Perform Operations on Subgroups of Data
POSTED BY: Nick Gaskill
You can also use GatherBy[...]:
{#[[1, 1]], Total[#[[All, 2]]]} & /@ GatherBy[data, #[[1]] &]
Apply Sort[...] to the final result if your dates will come out unsorted.
POSTED BY: Vitaliy Kaurov
That's better, yes.

Or even:
GatherBy[ data, First ]
POSTED BY: Arnoud Buzing
Does this work for you?


Map[
{#[[1, 1]], Total[#[[All, 2]]]} &,
Gather[list, SameQ[First[#], First[#2]] &]
]
POSTED BY: Arnoud Buzing
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