matlab array subsetting by indices

Question

Let's say I have a 3x3x3 Matlab array with members 1 to 27

a=reshape(1:27, [3 3 3])

I would like to create a subset of this with a syntax like

b=a(range1,range2,range3)

where for range1=range2=range3=1:2 I would get the members b(1,1,1) and b(2,2,2). i.e

b= [1 14]

Is it possible to do this just with indexing and without any functions (e.g. diag)? Thanks...

@Parag, sub2ind requires same size vectors for ranges. For example b=a(sub2ind(size(a),range1,range2,1:3)). That's why I am looking for doing it only with the indices... — ZZZ
– ZZZ, Commented Mar 15, 2013 at 23:53
range1, range2, and range3 have to be the same size because each corresponds to a dimension of the matrix a. For example, if range1 = [x1,x2,x3], range2 = [y1,y2,y3] and range3 = [z1,z2,z3] the values obtained will be a(x1,y1,z1), a(x2,y2,z2) and a(x3,y3,z3). So it wouldn't make sense for this function to take different sized vectors. In the example in your comment, what to do expect the answer to be? — Molly
– Molly, Commented Mar 16, 2013 at 1:50

Autonomous · Accepted Answer · 2013-03-15 23:29:33Z

1

It can be done with sub2ind function as follows:

b=a(sub2ind(size(a),range1,range2,range3)) ans: b=[1 14]

answered Mar 15, 2013 at 23:29

Autonomous

9,0751 gold badge41 silver badges79 bronze badges

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

2 Comments

ZZZ Over a year ago

sub2ind requires same size vectors for ranges. For example b=a(sub2ind(size(a),range1,range2,1:3)). That's why I am looking for doing it only with the indices...

Autonomous Over a year ago

If they are of same size, say 1:2, 1:2, 1:3, then how will you decide subscripts. Because when they are of equal size 1:2, subscripts will be (1,1,1) and (2,2,2)

Molly · Accepted Answer · 2013-03-15 23:32:11Z

The indexing can be done using sub2ind,

a(sub2ind(size(a),[1:2],[1:2],[1:2]))

if you want to avoid all functions, you could calculated the linear indices yourself...

Collectives™ on Stack Overflow

matlab array subsetting by indices

2 Answers 2

2 Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Related