Calculate differences between all values in vector

13 次查看（过去 30 天）
Swisslog
Swisslog 2014-4-7
评论： Mehri Mehrnia 2022-5-19
I'm trying to produce some code that will calculate the differences between nearly all values in a vector.
Specifically, say I have a vector [2 3 1 4]
Starting at 2 and moving through the vector, I need to calculate the difference between 2 and 3 (i.e. -1), 2 and 1, 2 and 4, then 3 and 1, 3 and 4, and then 1 and 4. I don't need to calculate the difference between, say, 3 and 2, and I'm only interested in the differences in one direction.
The vector I want to use the code on will be substantially bigger, and I'd like the output stored in a new, single column vector. I figured diff might provide a way forward, but can't see how to implement it specifying a 'lag'. Any help would be appreciated.

请先登录，再回答此问题。

采纳的回答

David Sanchez
David Sanchez 2014-4-7
my_vct = [2 3 1 4 5 6];
L = numel(my_vct);
tmp_vct = [my_vct(2:end) my_vct(end)];
x = my_vct - tmp_vct;
sol = zeros(L-1,L);
for k=2:L
tmp_vct = [my_vct(k:end) my_vct((L-k+2):end)];
sol(k-1,:) = my_vct - tmp_vct;
end
sol =
-1 2 -3 -1 -1 0
1 -1 -4 -2 0 0
-2 -2 -5 0 0 0
-3 -3 0 0 0 0
-4 0 0 0 0 0
  3 个评论
显示 1更早的评论
Swisslog
Swisslog 2014-4-7
...and
sol=sol(:);
sol(sol==0) = [];
to reduce to a single column I guess. Many thanks!

请先登录，再进行评论。

更多回答（2 个）

Jos (10584)
Jos (10584) 2014-4-7
编辑：Jos (10584) 2014-4-7
V = [2 3 1 4] ;
D1 = bsxfun(@minus,V(:), V(:).') % square form
% another option, only unique combinations, requires less memory
D2 = arrayfun(@(k) V(k:end)-V(k), 1:numel(k),'un',0)
D2 = [D2{:}]
  3 个评论
显示 1更早的评论
Soyy Tuffjefe
Soyy Tuffjefe 2021-8-14
编辑：Soyy Tuffjefe 2021-8-14
Thanks to Jos (10584) for your code...
I have a 5x1000 matrix (numerical entries),
M=[1 5 8 75 120;
1 25 18 5 10;
⋮ ⋮ ⋮ ⋮ ⋮
7 39 118 125 10]
and want to apply her or his code:
D2 = arrayfun(@(k) V(k:end)-V(k), 1:numel(k),'un',0)
D2 = [D2{:}
to every row of M, please, could anybody modify this code for this job.
Thanks in avanced!
Mehri Mehrnia
Mehri Mehrnia 2022-5-19
A great idea.
any body knows computation cost of bsxfun(@minus,V(:), V(:).')???
I mean linear or 2nd order or...
I work with arrays in order of millions, that's why it's important for me.

请先登录，再进行评论。

Mischa Kim
Mischa Kim 2014-4-7
Swisslog, you could use
pdist([2 3 1 4]',@(x,y) x-y)

类别

在 Help Center 和 File Exchange 中查找有关 Creating and Concatenating Matrices 的更多信息

标签

产品

Community Treasure Hunt

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

Start Hunting!

Translated by