how to swap some vector value?

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Mohammed Lamine Mekhalfia
编辑： Jan 2021-8-24
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.
Thanks a lot in advance for your contribution

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回答（3 个）

Star Strider
Star Strider 2021-8-24
Ran in:
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
Wan Ji 2021-8-24
编辑：Wan Ji 2021-8-24
A general answer is
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
Jan 2021-8-24
编辑：Jan 2021-8-24
Ran in:
% [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

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