Merge two columns into one

Hello everyone, A quick question: I want to merge two columns into one. What I've tried -

x = [1;2;3]; % (3x1 size) 
y = [5;6;7]; % (3x1 size)
XY = [x y];  % (3x2 size)
[ 1 5
  2 6
  3 8]

versus what i ultimately want

xy = [15;26;38]; % (3x1 size)

Any thoughts? I was looking into reshape as well but that would also give me a 3x2 variable. Thanks,

[Adam]

Where does [15;26;38] come from when you start with [1;2;3] and [5;6;7]? That's not what I would call 'merging'.

Reshape gives you whatever shape you tell it to provided there are the correct number of elements.

I assume you mean you want to concatenate the two columns of numbers, which would require you to convert them to chars I would think...e.g.

str2num( [num2str( x ) num2str( y )] )

I imagine there is a neater way though. str2num is not a pleasant function to have to use!

[OCDER]

Is there a mathematical workaround? For instance:

xy = 10*x+y 

xy =
  15
  26
  37

If not, yup, it gets pretty messy as Adam said.

[ numbers -> strings -> combined string -> number ] is the workaround.

str2double(sprintf('%d%d', x, y))

sprintf is generally faster if combining multiple numbers to a single string.

str2double is faster than str2num for some reason.

[Adam]

str2double doesn't use eval, which is good, but it wouldn't work in my solution. I can't remember off-hand what it resulted in, but it wasn't the required answer!

Answer 1

[Stephen23]

Ugly eval is not required, a simple use of sprint and sscanf is more efficient:

>> x = [1;2;3];
>> y = [5;6;8];
>> sscanf(sprintf('%d%d,',[x.';y.']),'%d,')
ans =
   15
   26
   38

This is more than four times faster than the accepted answer (1e4 iterations):

Elapsed time is 3.26133 seconds. % accepted answer
Elapsed time is 0.716072 seconds. % my answer

[Natasha Sekhon]

Ok, great! Yes, i 'm new to using Matlab and appreciate the talk about using eval.

[Stephen23]

@Natasha Sekhon: you might like to read this thread, it has a few points that are worth keeping in mind when learning MATLAB:

https://www.mathworks.com/matlabcentral/answers/228557-experts-of-matlab-how-did-you-learn-any-advice-for-beginner-intermediate-users