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question regarding totals

Posted 11 years ago
4 Replies
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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.
POSTED BY: Samuel Chen
4 Replies
Posted 11 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?

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