# Question about sorting an array column by column

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helen orins2021-9-27

I need to sort each column of a 1073x15 array for a heatmap in MATLAB.
[~,sortdices] = sort(choose_data(:,1),'ascend');
%choose_data = choose_data(:,sortdices);
for i=1:15
choose_data(:,i) = choose_data(sortdices,i)
end
this is my code. choose_data is the 1073x15 array. My output ends up being the first column sorted in ascending order, but the rest not. How do I fix it, such that all columns are sorted in ascending order? (Thank you for any help!)
##### 2 个评论显示隐藏 1更早的评论
helen orins 2021-9-27
Each column is sorted independently. So column 1, in ascending order. Done. Next, column 2, and so on. Hence the loop. So that's why I created the function. The rows are untouched.

### 回答（2 个）

the cyclist 2021-9-27

choose_data = sort(choose_data)
will sort every column independently. Ascending sorting is the default, so you don't need to specify that. (But it also doesn't hurt, and might make the code clearer.)
##### 2 个评论显示隐藏 1更早的评论
the cyclist 2021-9-27
Strange. Here is an example that illustrates that the syntax works:
M = magic(3)
M = 3×3
8 1 6 3 5 7 4 9 2
M = sort(M)
M = 3×3
3 1 2 4 5 6 8 9 7
Note that you do not need to do anything in a for loop. That one line of code will sort all columns of the array. You also don't need to do any indexing into the array.

Steven Lord 2021-9-27
Specify the dim input argument to the sort function.
A = magic(5)
A = 5×5
17 24 1 8 15 23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9
B = sort(A, 1)
B = 5×5
4 5 1 2 3 10 6 7 8 9 11 12 13 14 15 17 18 19 20 16 23 24 25 21 22
% Compare with
C = sort(A, 2)
C = 5×5
1 8 15 17 24 5 7 14 16 23 4 6 13 20 22 3 10 12 19 21 2 9 11 18 25
If you want to sort one of the columns and have the rest of the rows rearrange correspondingly see the sortrows function.
D = sortrows(A, 2) % sort by column 2
D = 5×5
23 5 7 14 16 4 6 13 20 22 10 12 19 21 3 11 18 25 2 9 17 24 1 8 15

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