Is there faster ranking for matrices than double sort()?

4 ビュー (過去 30 日間)
Marin Genov
Marin Genov 2022 年 9 月 16 日
編集済み: Marin Genov 2022 年 9 月 16 日
I have a uint16 matrix, where I want to determine the rank of each element with respect to its column in sorted form. The sort function doesn't quite do this, but using the second output twice does it. I need to repeat this routine many times in my code, and profiling reveals that it's by far the slowest part. So, I was wondering if there is a faster way to accomplish this (double sort() seems a bit of an overkill for this perhaps).
Here is a MWE:
M = 50;
m = 50;
n = 2000;
A = randi(M,m,n,'uint16'); % generate an example matrix
% Ranking via double sort():
tic;
[~,I] = sort(A,1);
[~,R] = sort(I,1);
toc;

採用された回答

Bruno Luong
Bruno Luong 2022 年 9 月 16 日
編集済み: Bruno Luong 2022 年 9 月 16 日
Not sure it is faster, but on the theorical complexity it is better (single sort).
A = randi(10,5,3)
A = 5×3
10 5 9 9 1 5 9 3 9 8 3 3 1 9 2
[~,I] = sort(A,1);
[m,n] = size(A);
R = zeros(m,n);
R(I+(0:n-1)*m) = repmat((1:m)',1,n)
R = 5×3
5 4 4 3 1 3 4 2 5 2 3 2 1 5 1
  9 件のコメント
Bruno Luong
Bruno Luong 2022 年 9 月 16 日
Are you sure? it looks fine to me for toy example
A = randi(10,5,3);
[~,I] = sort(A,1);
[m,n] = size(A);
% double sort
[~,R] = sort(I,1)
R = 5×3
1 4 5 3 1 1 4 3 2 5 2 3 2 5 4
% accumarray
R=accumarray(reshape(I+(0:n-1)*m,[],1),repmat((1:m)',n,1),[m*n,1]); % EDIT BUG FIX
R=reshape(R,m,n)
R = 5×3
1 4 5 3 1 1 4 3 2 5 2 3 2 5 4
Marin Genov
Marin Genov 2022 年 9 月 16 日
編集済み: Marin Genov 2022 年 9 月 16 日
@Bruno Luong: Apologies, I forgot to rename the R from the new method after copying the code, so MATLAB compared the original output again with the old output that was still in the workspace. Everything seems fine now. Many thanks!

サインインしてコメントする。

その他の回答 (0 件)

カテゴリ

Help Center および File ExchangeMatrices and Arrays についてさらに検索

製品


リリース

R2022a

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by