extend an array with repeated values until another array values matches MATLAB

Question

a=[2 3 4 7 9 12 15 18 22]
b=[2 7 15]

The result should be like this

c=[2 2 2  7 7 7 15 15 15];

The values should repeat until another matrix values matches. How can Matlab get me a solution for all problems related to this? Kindly help..

Can we assume that a and b are sorted to begin with?

Ben A.
– Ben A.

2012-07-17 19:29:15 +00:00
Commented Jul 17, 2012 at 19:29 — Ben A.
– Ben A., Commented Jul 17, 2012 at 19:29

H.Muster · Accepted Answer · 2012-07-17 20:02:08Z

2

Assuming that a and b are sorted, you can try this

c = b(sum(bsxfun(@(x,y) x >= y, a, b(:))));

This results in

c =
     2     2     2     7     7     7    15    15    15

Please note that this works only if b(1) == a(1). If b(1) < a(1), b(1) will be repeated although it does not match a(1) and if b(1) > a(1) an error is thrown because a subscript index is smaller than 1.

answered Jul 17, 2012 at 20:02

H.Muster

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Dr. Stanley Raj Over a year ago

Thank you for your reply....the previous post is enough for my work and it will be more useful for me...the condition b(1)==a(1) always satisfies..no problem.thank you very much

Isaac · Accepted Answer · 2012-07-17 19:43:06Z

1

Assuming that the first two numbers are always the same (otherwise what should the first number of the result be?):

prevj = b(1);
last = 1;
c = a;
for j = b(2:end)
    ind = find(c == j);
    c(last:ind-1) = prevj;
    last = ind;
    prevj = j;
end
c(last:end) = prevj;

Sorry about the messy code, but it seems to get the results you want (with a few assumptions).

answered Jul 17, 2012 at 19:43

Isaac

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