arrange indices

hi, if i have this vector

r=[2 4 18 5 6 15 3 4 16]; i need arrange index 3,6,9 with ascending, and each both previous index are arranged according for that as:

r=[5 6 15 3 4 16 2 4 18]; i.e just 3,6,.....are arranged with ascending and the index befor it are arranged according to third , sixth,..... i would to say ,this is just example i have too long vector

Answer 1

[Andrei Bobrov]

[ii,ii] = sort(r(3:3:end));
out = reshape(r(bsxfun(@plus,ii*3,(-2:0)')),1,[]);

OR:

out = reshape(sortrows(reshape(r,3,[])',3)',1,[]);

[huda nawaf]

thanks,

this is what i need , but what i have to do if need vector as:

r=[5 6 3 4 2 4];

i.e 15, 16, 18 are deleted

thanks in advance

[Image Analyst]

out(3:3:end) = []

[huda nawaf]

thanks,

but when try it with vector with length 8

i get error

ex.

s1=[1 3 4 5 62 3 5 7 ];

>> out(i,:) = reshape(sortrows(reshape(s1,3,[])',3)',1,[]);

??? Error using ==> reshape

Product of known dimensions, 3, not divisible into

total number of elements, 8.

what i ahve to do in this case?

[Image Analyst]

You violated your original description, where you had a multiple of three elements and you sorted the "third" ones, and moved them around to their new location, taking the prior two elements with them to their new locations. Now with 8 elements you have an extra two elements (at indexes 7 and 8) that don't have a third element associated with them at index 9. Please think about what you want to do in general and then share that.

[huda nawaf]

i want arrange the third , sixth, ninth,....elements with ascending , but when these elemnts are arranged the other elements that correspond with it it must be arranged also according to the

as example above

r=[2 4 18 5 6 15 3 4 16];

it must be as:

r=[5 6 15 3 4 16 2 4 18]

thanks

[huda nawaf]

what if need that

ex. r=[1 2 4 18 5 6 15 3 4 16];

if need 1 in same index and the other values as:

r=[1 5 6 15 3 4 16 2 4 18];

what will be changed in this command?

out = reshape(sortrows(reshape(r,3,[])',3)',1,[]);

[Andrei Bobrov]

out = [r(1),reshape(sortrows(reshape(r(2:end),3,[])',3)',1,[])];