# How can I sort an array of repeating elements

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mohan on 1 Apr 2013
Hi
I have the following array (20 by 2). The 1st column is node number and 2nd is temperature. The temperature is in descending order. There are 6 different values of temperatures. How can I sort this array such that it outputs;
set1 temp=670K nodes=10,14,15
set2 temp=668K nodes=385,431,432,440,441,442
set3 temp=655K nodes=649,650,959,960,961
set4 temp=654K nodes=80
set5 temp=653K nodes=89,90,651,652
set6 temp=646K nodes=646
ARRAY:
10 670.0
14 670.0
15 670.0
385 668.0
431 668.0
432 668.0
440 668.0
441 668.0
442 668.0
649 655.0
650 655.0
959 655.0
960 655.0
961 655.0
80 654.0
89 653.0
90 653.0
651 653.0
652 653.0
79 646.0
I hope the above is clear. Let me know if its not.
Mohan
mohan on 3 Apr 2013
Hi
The exact outputs I require is:
OUTPUT 1: group the nodes to sets but only when there are more than 1 node. see below.
*Nset, nset=set1
10, 14, 15
*Nset, nset=set2
385, 431, 432, 440, 441, 442
*Nset, nset=set3
649, 650, 959, 960, 961
*Nset, nset=set4
89, 90, 651, 652
OUTPUT 2: now combine the above information and temperature data and single node values. see below.
set1, 670
set2, 668
set3, 655
80, 654
set4, 653
79, 646
I hope the above is clear. Please get back to me if not.
Thanks
Mohan

Image Analyst on 1 Apr 2013
Did you try sortrows():
% Sort by column 2 in descending order.
sortedArray = sortrows(ARRAY, -2)

Brian B on 1 Apr 2013
It depends how you want to store the sets. If you are comfortable with cell arrays, you can create one vector with the unique temperatures, and then create a cell array of the same size such that each cell has the set of nodes withe the corresponding temperature:
temperatures = unique(ARRAY(:,2));
nodes = arrayfun(@(temp)ARRAY(ARRAY(:,2)==temp, 1),temperatures,'UniformOutput',0)

Andrei Bobrov on 1 Apr 2013
a = [10 670.0
14 670.0
15 670.0
385 668.0
431 668.0
432 668.0
440 668.0
441 668.0
442 668.0
649 655.0
650 655.0
959 655.0
960 655.0
961 655.0
80 654.0
89 653.0
90 653.0
651 653.0
652 653.0
79 646.0];
[b, ~, c] = unique(a(:,2),'stable');
out = [num2cell((1:max(c2))') num2cell(b) accumarray(c2,a(:,1),[],@(x){x})];