# How to get cumulative sum in yearly buckets

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Wendy Cameron on 17 May 2018
Commented: Wendy Cameron on 18 May 2018
I have several years of data and temperature in one table. I want to calculate a cumulative temperature sum which I've done simply as A.CumulativeTemp= cumsum(A.Temp);
My question is, how can get a cumulative temp for each year, i.e. so it gives a cumulative temperature for the entire 2016, then starts again at zero in the same column and does the same for 2017 and so on?
Kind regards, Wendy
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Wendy Cameron on 17 May 2018
Mostly my dates are in 1/1/2006 type format but I have made a year only column so there is just 2017 or 2016 that can be referred to. Wendy

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### Accepted Answer

Akira Agata on 17 May 2018
How about the following ?
% Read the data file and delete the answer column
opts = detectImportOptions('Reset Accum temp.xls');
T = readtable('Reset Accum temp.xls',opts);
T.AccumulatedTemperatureOfEachYear = []; % Remove the answer
% Apply cumsum function for each Year
T2 = varfun(@cumsum,T,'GroupingVariables','Year');
T = [T T2(:,'cumsum_Temperature')];
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Wendy Cameron on 17 May 2018
Thanks that works. I am now wondering how it could be done accumulating the temperatures from 1st July to 30th June perhaps. Every answer seems to generate another question!
Kind regards, Wendy

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### More Answers (3)

Ameer Hamza on 17 May 2018
One way to do this is follow
[group, uniqueYears] = findgroups(A.years)
yearSum = splitapply(@sum, A.Temp, group)
yearSummary = [uniqueYears, group];
Or you can also use accumarray as follow:
yearSum = accumarray(A.years, A.Temp);
##### 1 CommentShowHide None
Wendy Cameron on 17 May 2018
I've attached a very cut down file to try to explain my question. I want to get a column like the third column in the attached. i.e. the accumulation temperature is shown for each day of the year but resets at a certain date and starts accumulating from zero again from that date (not necessarily the end of the year).
I hope this explains the question a bit better.

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Andrei Bobrov on 17 May 2018
data = readtable('Reset Accum_temp.xls','range','A2:B32');
[~,~,c] = unique(data.Year);
N = accumarray(c,data.Temperature);
T = data.Temperature;
lo = [0;diff(data.Year)]~=0;
T(lo) = T(lo) - N(1:end-1);
data.AccumulatedTemperatureOfEachYear = cumsum(T);
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Wendy Cameron on 17 May 2018
Yes, well this certainly works. I could never have written it myself but I think I can see what you've done. Slowly I am learning. Thank you.

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Razvan Carbunescu on 17 May 2018
If using R2018a and wanting the final sum each year only can use groupsummary to get this more directly:
>> T = readtable('Reset Accum_temp.xls','range','A2:B32');
>> GT = groupsummary(T,'Year','sum','Temperature')
GT =
3×3 table
Year GroupCount sum_Temperature
____ __________ _______________
2015 10 267
2016 10 166
2017 10 208
You can use the date directly also with groupsummary
>> T.Date = datetime(T.Year,1,1); % reconstruct full Date
>> GT = groupsummary(T,'Date','year','sum','Temperature')
GT =
3×3 table
year_Date GroupCount sum_Temperature
_________ __________ _______________
2015 10 267
2016 10 166
2017 10 208
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Wendy Cameron on 18 May 2018
Thank you - this seems a very elegant solution and for my work I can see many applications. Unfortunately I don't have the 2018 version but hope to one day having seen this!
Regards, Wendy

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