how to return indices?

Question

Lilya 2022-6-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1738735-how-to-return-indices

评论： Lilya 2022-6-12

Hi,

I have a 3 dimensional data matrix (72*45*2109), and I need to extract all data less than 15. the final output should be a 3d matrix

I used the following lines, but the result is a vector. The point is to return the indices to have 3d matrix.

Any help would be greatly appreciated.

[r,c,v] = ind2sub(size(data),find(data >= 15));
l = data(sub2ind(size(data),r,c,v));

2 个评论
显示无隐藏无

DGM 2022-6-12

编辑：DGM 2022-6-12

You get a vector, because those are the indices of elements that you wanted -- only the indices you wanted.

Arrays need to be rectangular, without holes.

With that restriction, you'll have to decide what you want to fill all the area where there are elements you didn't want. It could be zero, NaN, etc. It's up to you and what the subequent code can accept without causing errors, since neither zero nor NaN are valid indices.

Lilya 2022-6-12

thanks for your comment

I've created an output nan matrix with the same dimension (72*45*2109), but all the output (r,c,v) are vectros as well

I don't know how to put them back in the output matrix

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Dyuman Joshi 2022-6-12

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1738735-how-to-return-indices#answer_983960

在 MATLAB Online 中打开

Based on your comment -

%random data
y=randi(30,2,3,4)
y = 
y(:,:,1) =

     7    17    10
    24    11    14


y(:,:,2) =

     3     2     6
    13    17     1


y(:,:,3) =

    26     3    14
    26    27     3


y(:,:,4) =

     7     5     4
     3     7    26
z=NaN(2,3,4);
z(y<15)=y(y<15)
z = 
z(:,:,1) =

     7   NaN    10
   NaN    11    14


z(:,:,2) =

     3     2     6
    13   NaN     1


z(:,:,3) =

   NaN     3    14
   NaN   NaN     3


z(:,:,4) =

     7     5     4
     3     7   NaN