# Logical indexing without for loop

5 ビュー (過去 30 日間)
Tyler 2016 年 4 月 19 日
コメント済み: Tyler 2016 年 4 月 19 日
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.

サインインしてコメントする。

### 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 件のコメント表示非表示 1 件の古いコメント
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.

サインインしてコメントする。

### 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.
##### 1 件のコメント表示非表示 なし
Tyler 2016 年 4 月 19 日

サインインしてコメントする。

### 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!

Translated by