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From: Robert Barrie on 22 Feb 2010 01:19
Hi All,

I have a column vector of numbers that I would like to extrapolate by "doubling up":

e.g. turn
2
4
6
8

into:
2
2
4
4
6
6
8
8

any ideas on an easy vectorised way to do this?

TIA,

Rob
From: Matt J on 22 Feb 2010 01:45


v=repmat([2; 4; 6; 8].',2,1);
v=v(:)
From: James Tursa on 22 Feb 2010 01:46
"Robert Barrie" <askme(a)ifuwant.com> wrote in message <hlt7kp$rut$1(a)fred.mathworks.com>...
> Hi All,
>
> I have a column vector of numbers that I would like to extrapolate by "doubling up":
>
> e.g. turn
> 2
> 4
> 6
> 8
>
> into:
> 2
> 2
> 4
> 4
> 6
> 6
> 8
> 8
>
> any ideas on an easy vectorised way to do this?
>
> TIA,
>
> Rob

x = [2;4;6;8];
y = [x x]';
y = y(:);

James Tursa
From: Robert Barrie on 22 Feb 2010 02:02
Thanks,

Though both of those options worked for x =[2;4;6;8], they didn't seem to work for x = 2:2:8??? (they were doubled but on top of each other, not 'sorted').

(the first way has [2;4;6;8] in the watch window, the 2nd has <4x1 double>)

any thoughts?

thx
From: James Tursa on 22 Feb 2010 02:23
"Robert Barrie" <askme(a)ifuwant.com> wrote in message <hlta5d$p7g$1(a)fred.mathworks.com>...
> Thanks,
>
> Though both of those options worked for x =[2;4;6;8], they didn't seem to work for x = 2:2:8??? (they were doubled but on top of each other, not 'sorted').
>
> (the first way has [2;4;6;8] in the watch window, the 2nd has <4x1 double>)
>
> any thoughts?
>
> thx

You specifically said "column" vector in your original post. x = 2:2:8 is not a column vector, it is a row vector. For row vectors you can use:

x = 2:2:8;
y = [x;x];
y = y(:);

James Tursa
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