Compare vectors of different lengths using end of shorter one when it ends

Say I have three vectors:

A = 1:10;

B = 1:5;

C = 1:15;

I want to do an operation using A and either B or C, but, when the shorter vector ends, I want to continue the operation using the last value of the shorter one until the longer one ends too. For example, if I want to add them:

A+B = [1+1,2+2,3+3,4+4,5+5,6+5,7+5,8+5,9+5,10+5];

A+C = [1+1,2+2,3+3,4+4,5+5,6+6,7+7,8+8,9+9,10+10,10+11,10+12,10+13,10+14,10+15];

How can I do this efficiently? Note that A is not always the shortest, so I need to identify which one is shorter as part of this. Thanks!

Answer 1

[Scott MacKenzie]

Someting like this perhaps:

A = 1:10;
B = 1:5;
C = 1:15;

nA = length(A);
nB = length(B);
nC = length(C);

% A + B
if nA < nB
    [A repelem(A(end),1,nB-nA)] + B
else
    A + [B repelem(B(end),1,nA-nB)]
end

ans = 1×10

2 4 6 8 10 11 12 13 14 15

% A + C
if nA < nC
    [A repelem(A(end),1,nC-nA)] + C
else
    A + [C repelem(C(end),1,nA-nC)]
end

ans = 1×15

2 4 6 8 10 12 14 16 18 20 21 22 23 24 25

[Dan Houck]

I hadn't thought to replicate the last element to bring them up to the same length. How would you do this if you had a cell array of many vectors of different lengths and you want to loop through them?

[Scott MacKenzie]

If the vectors are in a cell array (CA), then something like this would work:

A = 1:10;
B = 1:5;
C = 1:15;
CA = {A; B; C}

CA = 3×1 cell array
    {[               1 2 3 4 5 6 7 8 9 10]}
    {[                          1 2 3 4 5]}
    {[1 2 3 4 5 6 7 8 9 10 11 12 13 14 15]}

nA = length(CA{1});
nB = length(CA{2});
nC = length(CA{3});

% A + B
if nA < nB
    [CA{1} repelem(CA{1,end},1,nB-nA)] + CA{2}
else
    CA{1} + [CA{2} repelem(CA{2}(end),1,nA-nB)]
end

ans = 1×10

2 4 6 8 10 11 12 13 14 15

% A + C
if nA < nC
    [CA{1} repelem(CA{1}(end),1,nC-nA)] + CA{3}
else
    CA{1} + [CA{3} repelem(CA{3}(end),1,nA-nC)]
end

ans = 1×15

2 4 6 8 10 12 14 16 18 20 21 22 23 24 25

If there are lots of vectors in CA, you could build a loop that includes the logic above to add the elements in the first vector to the elements in each subsequent vector in the cell array.