Changing elements of vector with matrix

I have a question regarding a simple operation that I cant find an answer to. Hope that someone can help me.

I have a vector a:

a = zeros(1,10)

and a matrix b:

b = [1, 3; 6, 8]

I want to change elements of a into ones in accordance with the segments indicated by matrix b:

The result should be

1 1 1 0 0 1 1 1 0 0

When I try:

a(b(:,1):b(:,2)) = 1

I get

1 1 1 0 0 0 0 0 0 0

Best regards,

Michael

Answer 1

[Stephen23]

No loop required:

>> v = 1:numel(a);
>> x = any(v>=b(:,1) & v<=b(:,2), 1); % requires MATLAB >=R2016b
>> a(x) = 1
a =
   1   1   1   0   0   1   1   1   0   0

For earlier versions replace the logical comparisons with bsxfun.

Or just use one simple loop:

>> for k = 1:size(b,1), a(b(k,1):b(k,2)) = 1; end
>> a
a =
   1   1   1   0   0   1   1   1   0   0

[Michael Clausen]

Thank you for the quick reply, Ill try your loop.

I was hoping to do the manuvre without a loop, but I guess it is not possible?

[Stephen23]

"I was hoping to do the manuvre without a loop"

See my edited answer.

[Michael Clausen]

Thanks :-)

Answer 2

[Ashish Azad]

The syntax you are using is very ambiguous and will never work

Try

for i=1:length(b)

a(b(i,1):b(i,2))=1;

end

Let me know if this work

[Stephen23]

Do NOT use length for this code:

for i=1:length(b)

Consider what would happen if b only has one row.

The only robust solution is to use size and specify the dimension.

[Ashish Azad]

Yeah truly said Stephen, size would be robust option

Answer 3

[Alan Stevens]

One way as follows:

a =

     0     0     0     0     0     0     0     0     0     0

>> b

b =

     1     3
     6     8

>> a([b(1,1):b(1,2) b(2,1):b(2,2)]) = 1

a =

     1     1     1     0     0     1     1     1     0     0