Logical indexing without for loop
5 ビュー (過去 30 日間)
表示 古いコメント
Hi all,
This is probably a simple question, but I would love some input from those who can lend it. I have a vector [A] I would like to index according to a condition comparing the nth entry of A with the one following it (n+1).
For instance, if A is [1,2,3,4,5,6,7,6,5,4,3,2,1], and I would like to know which entries of A are larger than the entry preceding it, I would try to do the following:
for i = 1:size(A)
if i > 1
j = A(i) > A(i-1);
end
end
Where j = [0,1,1,1,1,1,1,0,0,0,0,0,0]
Is there a way to do this without using a loop? Any help would be appreciated, thank you.
0 件のコメント
採用された回答
Renato Agurto
2016 年 4 月 19 日
j = [0 A(2:end) > A(1:end-1)]
2 件のコメント
Walter Roberson
2016 年 4 月 19 日
You used A(1:end)-A(1:end-1) which subtracts two vectors of different sizes. Renato used A(2:end) for the first operation.
その他の回答 (1 件)
Walter Roberson
2016 年 4 月 19 日
[abs(diff(A)) > 0.001, false]
The false compensates for the fact that diff(A) is one shorter than A itself. You will find that in practice it is not a problem to use a logical index shorter than the array dimension, so for most purposes
abs(diff(A)) > 0.001
would be just as good.
参考
カテゴリ
Find more on Loops and Conditional Statements in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!