Finding sum of large array based on row values

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Poulomi Ganguli le 11 Août 2017
Commenté : Jan le 11 Août 2017
Hello, I have a big matrix where the 1st column varies for the year (1993 to 2014), 2nd column is month, 3rd column is day, 4th is hour, fifth min, sixth second and the last column is value. The value of 4th column varies from 0 to 23 hr, making a full day.
1993 4 2 0 0 0 2,44
1993 4 2 0 15 0 2,34
1993 4 2 0 30 0 2,21
1993 4 2 0 45 0 2,14
1993 4 2 1 0 0 2,04
1993 4 2 1 15 0 1,98
1993 4 2 1 30 0 1,92
1993 4 2 1 45 0 1,87
1993 4 2 2 0 0 1,79
1993 4 2 2 15 0 1,75
1993 4 2 2 30 0 1,73
1993 4 2 2 45 0 1,73
1993 4 2 3 0 0 1,72
1993 4 2 3 15 0 1,73
1993 4 2 3 30 0 1,78
1993 4 2 3 45 0 1,77
......................................................
......................................................
......................................................
2014 12 31 21 0 0 3,82
2014 12 31 21 15 0 3,89
2014 12 31 21 30 0 3,88
2014 12 31 21 45 0 3,89
2014 12 31 22 0 0 3,90
2014 12 31 22 15 0 3,85
2014 12 31 22 30 0 3,81
2014 12 31 22 45 0 3,74
2014 12 31 23 0 0 3,66
2014 12 31 23 15 0 3,56
2014 12 31 23 30 0 3,45
2014 12 31 23 45 0 3,34
I have to group the similar 4th row element (which varies from 0 to 23) and find out mean of the last column. So, the desired output would be:
1993 4 2 0 0 0 2.28
1993 4 2 1 0 0 1.95
1993 4 2 2 0 0 1.75
1993 4 2 3 0 0 1.75
.....................................................
.....................................................
2014 12 31 21 0 0 3,87
2014 12 31 22 0 0 3.82
Any help on this?
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José-Luis le 11 Août 2017
I'm gonna go ahead and assume that this is a text file.

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Réponse acceptée

alice le 11 Août 2017
Modifié(e) : alice le 11 Août 2017
[dateAndHour,~,index] = unique(data(:,1:4),'rows'); % find the hours present in the matrix and attribute each element of the matrix to one of these hours
hourlyMean = accumarray(index,data(:,7),[],@mean); % compute the hourly mean
output = [dateAndHour,zeros(size(dateAndHour,1),2),hourlyMean]; % build the output
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Jan le 11 Août 2017
Note that mean will reply the mean over the 2nd dimension, when an index occurs once only. See https://www.mathworks.com/matlabcentral/answers/352429-hourly-mean-for-my-data

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