Replace an element of a vector by also redefining the vector

Hi all,

I would like to replace some elements of a vector Vec that have indices idx with NaN, to create a new vector VecNaN. However, using the usual code below

 Vec(idx) = NaN;

redefines the vector Vec with the NaN elements. Instead I want to find a new vector VecNaN such that it is the same as Vec, but with the NaN elements in the indices idx.

Thanks for your help in advance,

KMT.

Answer 1

[Harry Vancao]

You could do the following:

vecNaN = vec; vecNaN(idx) = NaN;

[Jan]

+1. This is usually the most efficient solution. You could save the copy of the overwritten elements also, which is easier, when idx is a logical index vector:

x       = rand(1, 1000);
idx     = (x > 0.9);
y(idx)  = NaN;
y(~idx) = x(~idx);

This creates the vector y twice if the last element is not NaN. Better:

if idx(end)
  y(idx)  = NaN;
  y(~idx) = x(~idx);
else
  y(~idx) = x(~idx);
  y(idx)  = NaN;
end

Well, in most cases it is not worth the effort and Harry's suggestion is nice and efficient, although it "wastes" some time with copying elements, which are overwritten directly.

Answer 2

[Julie Kraus]

If I am understanding you correctly you want 2 vectors out, your original and a new vector with NaN's in idx locations.

VecNaN=Vec;
VecNaN(idx)=NaN;