CODEWITHSUNDEEP
matlab
dr_rk
dr_rk

Reputation: 4565

Filter Matrix in matlab

I have column vectors A and B: 

A'= [1 2 0 0 1 4]
B'= [1 2 3 4 5 6]

I would like to filter out the zeros in A and remove corresponding elements in B and have them as: 

A' = [1 2 1 4] 
B' = [1 2 5 6]

I know there is a quick MATLAB command to do this, but cant figure it out.

Upvotes: 3

Views: 3338

Answers (4)

Victor Bai
Victor Bai

Reputation: 103

Another alternative is to remove the 0 element in A:

A0=A==0;
A(A0)=[]; 
B(A0)=[];

Howerver as @RodyOldenhuis said, A(A0)=[] is slower than A=A(A0). So, when large loop is involved, or size of A is very large, A(A0)=[] should be avoided to use.

Upvotes: 1

learnvst
learnvst

Reputation: 16195

You can condense the logical indexing solutions further by removing the intermediate variable and changing the syntax slightly.

B=B(~~A)
A=A(~~A)

The only slight possible pitfall with removing an intermediate variable (i.e. nz=~~A) is that you have to remember to change B before changing A. This pitfall can be negated by converting the operation into a single command - the new values are not assigned to the variables until the right-hand-side of the expression has been evaluated. 

[A,B] = deal(A(~~A),B(~~A))

Zen (if you're looking for the smallest amount of command characters), although I concur that efficiency might suffer (see comment).

Upvotes: 2

Paul R
Paul R

Reputation: 212969

You can just do it like this:

> A = [1 2 0 0 1 4]
A =

   1   2   0   0   1   4

> B = [1 2 3 4 5 6]
B =

   1   2   3   4   5   6

> V = find(A~=0)        % get the indices for which A <> 0 
V =

   1   2   5   6

> A = A(V)              % select elements from A
A =

   1   2   1   4

> B = B(V)              % select elements from B
B =

   1   2   5   6

>

Upvotes: 1

Rody Oldenhuis
Rody Oldenhuis

Reputation: 38032

The quickest, easiest way is by using logical indexing: 

A = [1 2 0 0 1 4].';
B = [1 2 3 4 5 6].';

nz = (A ~= 0); %# logical matrix for non-zeros in A

A = A(nz)      %# non-zeros of A
B = B(nz)      %# corresponding elements in B

Another way is the slightly slower

nz = find(A); %# vector of linear indices to non-zero elements

A = A(nz)     %# non-zeros of A
B = B(nz)     %# corresponding elements in B

Upvotes: 5

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