# how to swap some vector value?

9 views (last 30 days)
Mohammed Lamine Mekhalfia on 24 Aug 2021
Edited: Jan on 24 Aug 2021
Dear all
I have the following vector
S=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 ...... ]
what I would like to do is to change 1 and 2 position to be after 10 then to 11 and 12 after 20 and etc.
so S will be like S= [3 4 5 6 7 8 9 10 1 2 13 14 15 16 17 18 19 20 11 12 ....]
I hope that the problem is well explained.

Star Strider on 24 Aug 2021
Use the reshape and circshift functions:
S=[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20]
S = 1×20
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Sr = reshape(S,10,[])
Sr = 10×2
1 11 2 12 3 13 4 14 5 15 6 16 7 17 8 18 9 19 10 20
Src = circshift(Sr,-2,1)
Src = 10×2
3 13 4 14 5 15 6 16 7 17 8 18 9 19 10 20 1 11 2 12
Result = reshape(Src,1,[])
Result = 1×20
3 4 5 6 7 8 9 10 1 2 13 14 15 16 17 18 19 20 11 12
Note — ‘S’ must always have a length that is an integer multiple of 10 for this to work. An alternative to reshape if that is not the situation is the Signal Processing Toolbox buffer function, however the results of the last column might not be the desired result.
.

Wan Ji on 24 Aug 2021
Edited: Wan Ji on 24 Aug 2021
S = 1:100; %
count = 1;
copyLength = 2; %
copyStep = 10; % copyStep>copyLength
while count<=numel(S)-copyLength
if(count==1)
copySeg = S(count:count+copyLength-1);
S(count:count+copyLength-1) = [];
count = count + copyStep - copyLength;
else
copyTemp = S(count:count+copyLength-1);
S(count:count+copyLength-1) = copySeg;
copySeg = copyTemp;
count = count + copyStep;
end
end
if(count-1<=numel(S))
nLen = count + copyLength -1 - numel(S);
S = [S, ones(1,nLen)];
S(count:count+copyLength-1) = copySeg;
end

Jan on 24 Aug 2021
Edited: Jan on 24 Aug 2021
% [EDITED] Now working if S has not a multiple of 10 elements:
S = 1:25;
a = 2; % Move 2 elements
b = 10; % in blocks of 10
v = 0:numel(S) - 1;
k = rem(v + a, b) + 1 + b * floor(v / b);
T = S(k(k <= numel(S)))
T = 1×23
3 4 5 6 7 8 9 10 1 2 13 14 15 16 17 18 19 20 11 12 23 24 25

### Categories

Find more on General Applications in Help Center and File Exchange

R2018a

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!