# Sorting big data in matlab

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zafar khan on 2 Feb 2017
Commented: Walter Roberson on 2 Feb 2017
I have energy data with more than 25 million rows and 3 columns, the data looks like
1000 19506 .5
1000 19501 .5
. . .
1001 19500 .6
. . .
. . .
1999 19509 .4
. . .
1999 73048 .4]
I require to sort this data such that for each meter ID i.e. 1000-1999 (all 1000 meters) i get load arranged in a time series. The first three digit of time code show the day whereas the last two digits range from 0-48 showing 24 hours every half hours. I can sort the data according to meter ID but this does not arrange it according to time series. I am struggling to find a solution to find a technique to auto arrange the data such that it presents something like this;
meter ID 1000 [19501 19502 .......................... 73048 .5 1.5............................ 2.5] and so on for all meter IDs. It is easy to solve in excel using filters, however given the amount of data, excel is not able to open this file. Any recommendation.

Walter Roberson on 2 Feb 2017
sortrow(YourData, [1 2])
zafar khan on 2 Feb 2017
Sorting is one part and thank you for that. Any idea about rearranging because it is very difficult to go through some 25000 rows to find the next meter ID?
Walter Roberson on 2 Feb 2017
Ah, I was able to find a way to do it without any explicit loops:
[unique_ids, ~, uidx] = unique(sorted_rows(:,1));
grouped_rowidx = accumarray( uidx, (1:size(sorted_rows,1)), [], @(R) {R}, {});
grouped_rows = cellfun(@(R) sorted_rows(R,:), grouped_rowidx, 'Uniform', 0);