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How to count the duplicate id's within a group of a table?

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Faustino Quintanilla
回答： Peter Perkins 2017-11-29
Can a counter be added to a table for individual groups? For example:
  • equipment_id, date, group_id, count
  • 736694, 5/1/2017, 1, 1
  • 736694, 5/1/2016, 1, 2
  • 736694, 5/1/2015, 1, 3
  • 736694, 5/1/2014, 1, 4
  • 736789, 5/1/2016, 2, 1
  • 736789, 5/1/2015, 2, 2
  • 736789, 5/1/2015, 2, 3
  • 736910, 5/1/2017, 3, 1
  • 736910, 5/1/2017, 3 , 2
I am trying to view the last date entry for each equipment id.
  2 个评论
MHZ
MHZ 2017-11-27
Why do you need a counter? Search for the ID, then ask for the biggest date.
Faustino Quintanilla
Faustino Quintanilla 2017-11-27
There are other columns, that I did not show. Would this still work? What do you use search ID and biggest date?

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回答（1 个）

Peter Perkins
Peter Perkins 2017-11-29
If the table is already sorted by date and ID (use sortrows), then it's straight-forward:
>> t
t =
9×3 table
equipment_id date group_id
____________ __________ ________
736694 05/01/2017 1
736694 05/01/2016 1
736694 05/01/2015 1
736694 05/01/2014 1
736789 05/01/2016 2
736789 05/01/2015 2
736789 05/01/2015 2
736910 05/01/2017 3
736910 05/01/2017 3
>> groupCounts = accumarray(t.group_id,1)
groupCounts =
4
3
2
>> t.counter = repelem((1:3)',groupCounts)
t =
9×4 table
equipment_id date group_id counter
____________ __________ ________ _______
736694 05/01/2017 1 1
736694 05/01/2016 1 1
736694 05/01/2015 1 1
736694 05/01/2014 1 1
736789 05/01/2016 2 2
736789 05/01/2015 2 2
736789 05/01/2015 2 2
736910 05/01/2017 3 3
736910 05/01/2017 3 3
If you don't want to sort the table for some reason, then use rowfun: use group_id as a GroupingVariable, use date as an InputVariable, and make a function that returns a permutation of 1:n, "unsorted" by a column of dates.

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