binary array in MATLAB

Question

if i have an initial array A of twenty numbers in the order 1 to 20,

 A = [1,2,3,4,5,...,20]

and have another random array B:

  B = [1, 15, 3, 20, 7]

and want to output a column vector C of the form

  C = [1 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 1]

Note that C has a 1 at the indices at which B has a value.

I have tried the following:

n=20;
C = zeros(n, 1);
for i=1:length(B)
   C(B(i))=1;
end

What A has got to do with anything?

Eitan T
– Eitan T

2012-06-12 07:03:15 +00:00
Commented Jun 12, 2012 at 7:03 — Eitan T
– Eitan T, Commented Jun 12, 2012 at 7:03

Gunther Struyf · Accepted Answer · 2012-06-12 07:39:22Z

2

in a one-liner:

full(sparse(B,1,1,max(B),1))

and you could also drop the full function, most matlab matrix operation can deal with sparse matrices. But of course it depends on what you actually want to do.

answered Jun 12, 2012 at 7:39

Gunther Struyf

11.2k2 gold badges36 silver badges58 bronze badges

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

Comments

Amro · Accepted Answer · 2012-06-12 13:15:32Z

2

Another one-liner:

C = accumarray(B(:), 1, [], @(x)1)

edited Jun 12, 2012 at 13:15

answered Jun 12, 2012 at 13:03

Amro

125k25 gold badges250 silver badges466 bronze badges

3 Comments

Simon Over a year ago

Wrap it in logical() in case there are non-unique values in B.

Amro Over a year ago

@Simon: good catch, thank you. I solved it a slightly different way (to keep the result of type double).

Gunther Struyf Over a year ago

+1: accumarray is actually specifically made just for these kind of things, why didn't I think of that :p

Andrey Rubshtein · Accepted Answer · 2012-06-12 06:46:12Z

1

Here is a vectorized solution:

Firstly, initialize C

   C = zeros( max(B),1);

Then use array indexing:

   C(B) = 1;

answered Jun 12, 2012 at 6:46

Andrey Rubshtein

21k11 gold badges73 silver badges106 bronze badges

Collectives™ on Stack Overflow

binary array in MATLAB

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related