finding values located in one column in a multidimensional array

Question

I'm trying to find values in a multidimensional array which are only in one column. I can find the correct values when searching the entire multidimensional array. But if I try and limit the find in the multidimensional array to say just the second column the values are not the expected ones.

example of code and correct output:

A = [2 4 6; 8 10 12]
A(:,:,2) = [5 7 9; 11 13 15]
A(:,:,3) = [55 4 55; 167 167 154]

[row,col,page]=ind2sub(size(A), find(A(:,1,:)==4))

row =1,1
col =2,2
page =1,3

But If I try and limit the find to just the second column using these commands

[row,col,page]=ind2sub(size(A), find(A(:,2,:)==4)) 

row =1,1
col =1,3
page =1,1

I get values that are different from the expected ones. I'm trying to limit the multidimensional find to search all pages, all rows, and one specific column. The output should be the same as the first example. How can I fix this?

From what I have understood, you are looking to basically find the row and page numbers, when searching along a specific column. Thus, you can focus on finding just the row and page numbers. You can use this - [row,~,page]=ind2sub([size(A,1) 1 size(A,3)],find(A(:,col_num,:)==4)), where col_num would be the column number that you are searching along. The trick is to use 1 instead of size(A,2). — Divakar
– Divakar, Commented Jun 16, 2014 at 17:03

Luis Mendo · Accepted Answer · 2014-06-16 21:29:51Z

3

With [m,n,o]=size(A), you are using A(:,2,:)==4 which is a matrix n*1*o. ind2sub expects a n*m*o matrix. Typical approach is using a mask:

mask=false(size(A));
mask(:,2,:)=true;
[i,j,k]=ind2sub(size(A), find((A(:,:,:)==4)&mask))

The mask selects the entries you are interested in.

edited Jun 16, 2014 at 21:29

Luis Mendo

113k13 gold badges80 silver badges154 bronze badges

answered Jun 16, 2014 at 17:02

Daniel

36.8k3 gold badges38 silver badges73 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Community · Accepted Answer · 2017-05-23 12:05:32Z

1

Daniel's answer works by defining a mask and then searching throughout the whole array with that mask applied. The following limits the search to the desired column, and thus may be faster for large arrays:

col = 2; %// desired column
[row, page] = ind2sub([size(A,1) size(A,3)], find(A(:,col,:)==4));

If you need col as a vector the same size as row and page, you can of course achieve it with col = repmat(col,size(row)).

edited May 23, 2017 at 12:05

CommunityBot

11 silver badge

answered Jun 16, 2014 at 21:31

Luis Mendo

113k13 gold badges80 silver badges154 bronze badges

Collectives™ on Stack Overflow

finding values located in one column in a multidimensional array

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related