# How to substitute one value in vector by vector?

1 view (last 30 days)
Premysl Stastny on 23 Sep 2021
Answered: Matt J on 23 Sep 2021
Hello,
I have got a vectro x=(-1 1 -1 1) and I need to replace positions containing -1 for a vector (1 2 3) and positions containing 1 for a vector (3 2 1). so the result should be x=(1 2 3 3 2 1 1 2 3 3 2 1).
Could somebody help me?
Thanks a lot

KSSV on 23 Sep 2021
Edited: KSSV on 23 Sep 2021
x=[-1 1 -1 1] ;
iwant = cell(1,length(x)) ;
for i = 1:length(x)
if x(i) == -1
iwant{i} = [1 2 3 ];
elseif x(i) == 1
iwant{i} = [3 2 1] ;
end
end
iwant = cell2mat(iwant)
iwant = 1×12
1 2 3 3 2 1 1 2 3 3 2 1
%% No loop
% No loop
x=[-1 1 -1 1] ;
iwant = cell(1,length(x)) ;
iwant(x==1) = {[3 2 1]} ;
iwant(x==-1) = {[1 2 3]} ;
iwant = cell2mat(iwant)
##### 1 CommentShowHide None
Premysl Stastny on 23 Sep 2021
Thank you!

### More Answers (4)

Matt J on 23 Sep 2021
Edited: Matt J on 23 Sep 2021
x=[-1 1 -1 1];
idx=(x==1);
X=nan(3,numel(x));
X(1,idx)=3;
X(2,idx)=2;
X(3,idx)=1;
X(:,~idx)=4-X(:,idx);
X=X(:).'
X = 1×12
1 2 3 3 2 1 1 2 3 3 2 1

Matt J on 23 Sep 2021
x=[-1 1 -1 1];
i=(x+3)/2;
V=[1 2 3;3 2 1].';
X=reshape( V(:,i) ,1,[])
X = 1×12
1 2 3 3 2 1 1 2 3 3 2 1

Matt J on 23 Sep 2021
x=[-1 1 -1 1];
x=strrep(10*x,10,[3,2,1]);
Warning: Inputs must be character vectors, cell arrays of character vectors, or string arrays.
x=strrep(x,-10,[1,2,3])
Warning: Inputs must be character vectors, cell arrays of character vectors, or string arrays.
x = 1×12
1 2 3 3 2 1 1 2 3 3 2 1

Matt J on 23 Sep 2021
x=[-1 1 -1 1];
X=kron(-x,[1,2,3]);
X=X+4*(X<0)
X = 1×12
1 2 3 3 2 1 1 2 3 3 2 1