How to find index in a single array?

Question

J Yadav 2019-1-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/438689-how-to-find-index-in-a-single-array

评论： J Yadav 2019-1-8

Hi,

I have two column vectors A=(3, 4, 6, 9, 12, 34, 56, 99, 105, 190)' and B=(4, 12, 34, 56)' both are sorted in increasing order. And a bbig matrix D of size mxn, where m is no. of rows in A.

Purpose: is to divide the matrix D into two segments ,

a) matrix E which has 4 rows (=number of rows in B) which are the 2nd, 5th, 6th.. rows of matrix D

and

b) matrix F which has 6 rows (= numbers of rows in A minus number of rows in B) which are 1st, 3rd, 4th, 6th, ...etc rows of D,

So basically the row numbers given bby A has to divided into B and notB.

Here's what I am doing:

I need to find out the placement of each element of B in A. So I am using :

for i=size(B,1)
    C(i,1) = find(B(i,1)==A)
end

Question 1: Is there a way to vectorise this process and avoid the LOOP

After that I want to locate the row indexed by B and not B in a mXn matrix D, so I am using

rowEindex=1
rowFindex=1
for j=1:size(B,1)
    if A(j,1)==B
        E(rowEindex,:) = D(j,:)
        rowEindex = rowEindex+1
    else
        E(rowFindex,:) = D(j,:)
        rowFindex = rowFindex+1
end

Question 2: Is there a way to speed up this process, again without using the LOOP

many thanks for your response.

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Stephen23 2019-1-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/438689-how-to-find-index-in-a-single-array#answer_355442

编辑：Stephen23 2019-1-8

Simpler:

A = [3;4;6;9;12;34;56;99;105;190];
B = [4;12;34;56];
D = randi(999,200,7); % fake data
E = D(B,:);
F = D(setdiff(A,B),:);

3 个评论
显示 1更早的评论隐藏 1更早的评论

Stephen23 2019-1-8

@SHUBHAM GUPTA: you are right, I fixed that now.

J Yadav 2019-1-8

I have changed the question slightly, bbut your answer to use setdiff is helpful. Thanks,

请先登录，再进行评论。

Answer 2

Shubham Gupta 2019-1-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/438689-how-to-find-index-in-a-single-array#answer_355420

在 MATLAB Online 中打开

Try this :

A=[3, 4, 6, 9, 12, 34, 56, 99, 105, 190]';
B=[4, 12, 34, 56]' ;
D=[1:200;1:200;1:200;1:200]';
[val,ind]=intersect(A,B);
E=D(val,:);
A(ind)=[];
F=D(A,:);

I hope this helps.