Bed of Nails from vectors - inverse of find()?

조회 수: 2 (최근 30일)
Douglas Anderson
Douglas Anderson 2018년 2월 27일
댓글: Jos (10584) 2018년 2월 28일
Hello,
I would like to do the following:
X = zeros(N,M); % Say N = 50, M = 100
Then have N sets of indices, one for each row of X:
a(1,:) = [ 1 5 10 12 19 32 56 ...]; % These may vary substantially
a(2,:) = [ 1 7 14 19 29 45 76 ...];
...
These are then indices that will indicate where there should be a "1" in each row of X.
Is there a function that will take the indices and then put a "1" in an array? This is kind of like the inverse of find().
Thanks!
Doug Anderson
  댓글 수: 2
Jos (10584)
Jos (10584) 2018년 2월 27일
As your variable a is a N-by-K matrix, this assumes that all rows of X will hold K ones. Is that so?
Douglas Anderson
Douglas Anderson 2018년 2월 27일
Yes, that is true.

댓글을 달려면 로그인하십시오.

채택된 답변

Jos (10584)
Jos (10584) 2018년 2월 27일
% input
N = 5 ; M = 4 ;
a = [1 3 ; 2 4 ; 1 4 ; 1 2 ; 3 4]
% engine in one line
XX = full(sparse(repmat(1:N, size(a,2), 1)', a, 1,N,M))
  댓글 수: 2
Douglas Anderson
Douglas Anderson 2018년 2월 27일
Thanks to everyone. Of course, this is only the deepest level of a bunch of calculations to determine the "a" values, so this one-line engine is nice.
Can you tell me why this works? :) Thank you!
Jos (10584)
Jos (10584) 2018년 2월 28일
This might not be the most efficient way though.
See the documentation of sparse for more details.

댓글을 달려면 로그인하십시오.

추가 답변 (2개)

Sean de Wolski
Sean de Wolski 2018년 2월 27일
for ii = 1:size(x, 1)
x(ii, a(ii,:)) = 1;
end

Jos (10584)
Jos (10584) 2018년 2월 27일
N = 5 ; M = 4 ;
a = [1 3 ; 2 4 ; 1 4 ; 1 2 ; 3 4]
X = zeros(N,M)
X(sub2ind([N M], repmat(1:N, size(a,2), 1)', a)) = 1

카테고리

Help CenterFile Exchange에서 Simulink에 대해 자세히 알아보기

제품

Community Treasure Hunt

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

Start Hunting!

Translated by