🚀 go-pugleaf

In article <1k5hf2INNlgs@shelley.u.washington.edu>
phantom@stein2.u.washington.edu (The Phantom) writes in response to:

>   reese@vax.oxford.ac.uk, who wrote:
>
>   >I want to take two vectors and combine them, e.g.
>   >[ a b c d e]  and [ f g h i j ] 
>   >become  [ a f b g c h d i e j ]
>   >
>
>   say a=[ a b c d e ] and b=[ f g h i j ] -- an easy way to do this would be
>   using ...
>
>   len=length(a);			%assuming length(a), length(b) are equal
>   FOR count=1:len,
>	   c((count*2)-1)=a(count);
>	   c((count*2)=b(count);
>   END
>
>   that seems to work, anyway. just work with the commands for picking out 
>   certain matrix spots and FOR loops, and you should be able to comprise 
>   something that works both ways.
>
>   mt


How about a method which avoids the FOR loop:

c = [a;b];c = c(:)'  to go from a = [a b c ...] b = [f g h  ...] to 
                     c = [a f b g c h ...]

and a = c(1:2:length(c));b = c(2:2:length(c)); to unscramble.


Joe (joeb@atmos.washington.edu)

In article <1993Jan26.182616.11550@vax.oxford.ac.uk> reese@vax.oxford.ac.uk writes:
>
>
>I want to take two vectors and combine them, e.g.
>[ a b c d e]  and [ f g h i j ] 
>become  [ a f b g c h d i e j ]
>

say a=[ a b c d e ] and b=[ f g h i j ] -- an easy way to do this would be
using ...

len=length(a);			%assuming length(a), length(b) are equal
FOR count=1:len,
	c((count*2)-1)=a(count);
	c((count*2)=b(count);
END

that seems to work, anyway. just work with the commands for picking out 
certain matrix spots and FOR loops, and you should be able to comprise 
something that works both ways.

mt

In article <1k5hf2INNlgs@shelley.u.washington.edu> phantom@stein2.u.washington.edu (The Phantom) writes:

   In article <1993Jan26.182616.11550@vax.oxford.ac.uk> reese@vax.oxford.ac.uk writes:
   >
   >
   >I want to take two vectors and combine them, e.g.
   >[ a b c d e]  and [ f g h i j ] 
   >become  [ a f b g c h d i e j ]
   >

   say a=[ a b c d e ] and b=[ f g h i j ] -- an easy way to do this would be
   using ...

   len=length(a);			%assuming length(a), length(b) are equal
   FOR count=1:len,
	   c((count*2)-1)=a(count);
	   c((count*2)=b(count);
   END


One of the advantages of matlab is the vector subscripts (do loops are
not very efficient, and can normally be avioded), a better approach
is:-

(again assuming that the vectors are the same length, and called a and
b)

c([1:2:2*length(a),2:2:2*length(a)])=[a,b];

A more general solution for vectors of different lengths is:-

i=length(a);j=length(b);
if i>j
 c([1:2:2*j,j+[j+1:i],2:2:(2*j)])=[a,b];
else
 c([1:2:2*i,2:2:(2*i),i+[i+1:j]])=[a,b];
end  

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Schlumberger Cambridge Research          Tel/fax: 0223-325303 / 0223-311830
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In article <1k5hf2INNlgs@shelley.u.washington.edu> phantom@stein2.u.washington.edu (The Phantom) writes:
>In article <1993Jan26.182616.11550@vax.oxford.ac.uk> reese@vax.oxford.ac.uk writes:
>>
>>
>>I want to take two vectors and combine them, e.g.
>>[ a b c d e]  and [ f g h i j ] 
>>become  [ a f b g c h d i e j ]
>>
>
>say a=[ a b c d e ] and b=[ f g h i j ] -- an easy way to do this would be
>using ...
>
>len=length(a);			%assuming length(a), length(b) are equal
>FOR count=1:len,
>	c((count*2)-1)=a(count);
>	c((count*2)=b(count);
>END
>
>that seems to work, anyway. just work with the commands for picking out 
>certain matrix spots and FOR loops, and you should be able to comprise 
>something that works both ways.
>
>mt
>

Try the following:

% assignment of your vector
x = ['a' 'b' 'c' 'd' 'e'];
y = ['f' 'g' 'h' 'i' 'j'];
% assign an index vector
ind = [1:length(x)];
%assign the vector
z(ind*2-1) = x;
z(ind*2) = y;

%reverse assignment
%assign an index in a reverse way:
ind2 = [length(x) : -1 : 1];
%assign the vector
z2(ind*2-1) = x(ind2);
z2(ind*2) = y(ind2);


Actually, the contents of ind and ind2 can be any number in the index range.
I believe the example shows the most efficient and flexible way to use MATLAB.

In article <1k5hf2INNlgs@shelley.u.washington.edu> phantom@stein2.u.washington.edu (The Phantom) writes:
>In article <1993Jan26.182616.11550@vax.oxford.ac.uk> reese@vax.oxford.ac.uk writes:
>>
>>
>>I want to take two vectors and combine them, e.g.
>>[ a b c d e]  and [ f g h i j ] 
>>become  [ a f b g c h d i e j ]
>>
>
>say a=[ a b c d e ] and b=[ f g h i j ] -- an easy way to do this would be
>using ...
>
>len=length(a);			%assuming length(a), length(b) are equal
>FOR count=1:len,
>	c((count*2)-1)=a(count);
>	c((count*2)=b(count);
>END
>
>that seems to work, anyway. just work with the commands for picking out 
>certain matrix spots and FOR loops, and you should be able to comprise 
>something that works both ways.
>
>mt
>

Try to avoid using slow FOR loops if you can.
Here is a neat way which is faster

c(2:2:2*length(b))=b;
c(1:2:length(c))=a;

Ron Dilsavor
dilsavor@ee.eng.ohio-state.edu

In article <1993Jan26.182616.11550@vax.oxford.ac.uk> reese@vax.oxford.ac.uk writes:
>
>
>I want to take two vectors and combine them, e.g.
>[ a b c d e]  and [ f g h i j ] 
>become  [ a f b g c h d i e j ]
>
>Does anyone know a quick and easy way to do this, and the reverse of
>it?  Thanks in advance for your help!
>
>Jason


Jason,

Try this for 2 equal length input vectors:

>> v1 = [1 2 3];                  % create a vector for each
>> v2 = [4 5 6];                  %  operand
>> inx = 1:length([v1,v2]);       % create an indexing vector equal
>> inx = rem(inx,2);              %  to the summed length
>> result = zeros(size(inx));     % allocate the result vector
>> result(inx) = v1;              % put the v1 at odd indices
>> result(~inx) = v2;             % fill in the even with v2
>> result

result =
     1    4    2    5    3    6

>> result(inx)                    % retrieve v1

result =

     1    2    3

>> result(~inx)                   % retrieve v2

result =

     4    5    6


Hope this helps,

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