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Mathematica Wolfram Language

question regarding totals

Samuel Chen

Posted 12 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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Arnoud Buzing, Wolfram Research

Posted 12 years ago

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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Vitaliy Kaurov, WOLFRAM Research

Posted 12 years ago

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

2

Arnoud Buzing, Wolfram Research

Posted 12 years ago

That's better, yes. Or even: GatherBy[ data, First ]

POSTED BY: Arnoud Buzing

1

Nick Gaskill

Posted 12 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

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