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replace elements in an Array with other elements

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hi all,
i have the folwing situation:
i have an array:
A=[1 2 3 4 4 4 5 8 7 4 6 4]
i want to find the element equal to the value 4.
I do this:
index=find(A==4)
i want now to replace the element with this index with the previous value. it means i want to get:
A_new=[1 2 3 3 3 3 5 8 7 7 6 6].
i did it with a loop. is there any method without loop?
thank you

Risposta accettata

Guillaume
Guillaume il 20 Lug 2015
While it may be possible to do it without a loop, with a combination of diff, find and possibly cumsum it's going to be a lot more obscure than a simple loop and probably not any more efficient.
The simplest loop would be:
for idx = find(A == 4)
A(idx) = A(idx-1);
end
which also works for consecutive elements to replace.

Più risposte (3)

Walter Roberson
Walter Roberson il 20 Lug 2015
A_new = A;
A_new(index) = A(index-1);
This will fail if the very first thing was a 4, as there is no "previous" for the first element.
  1 Commento
Guillaume
Guillaume il 20 Lug 2015
This also fails on the example given, when there are consecutive elements to replace.

Accedi per commentare.


Sean
Sean il 20 Lug 2015
Modificato: Sean il 20 Lug 2015
A=[1 2 3 4 4 4 5 8 7 4 6 4]
idx = find(A~=4);
B = interp1(idx,A(idx),1:numel(A),'previous','extrap')
Gotta love the 'previous' and 'next' options added to interp1 a few releases ago!

Shashank
Shashank il 14 Giu 2018
How can I copy paste 2nd element to 3rd, 3rd to 4th and so on.. A=[1,2,3,4,5,6,7]; A_New=[1,2,2,3,3,4,4,5,5,6,6,7]; ---> Required

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