question regarding totals

Questions
1

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

2

Does this work for you?

Map[
 {#[[1, 1]], Total[#[[All, 2]]]} &, 
 Gather[list, SameQ[First[#], First[#2]] &]
 ]
3

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.

4

That’s better, yes.

Or even:

GatherBy[ data, First ]
5

There’s also a useful how-to in Documentation that talks about this…

How to Perform Operations on Subgroups of Data