replace elements in an Array with other elements

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Rica
Rica 2015-7-20
评论： Juan Jiménez 2020-6-22
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

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采纳的回答

Guillaume
Guillaume 2015-7-20
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.

更多回答（3 个）

Walter Roberson
Walter Roberson 2015-7-20
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 个评论
Guillaume
Guillaume 2015-7-20
This also fails on the example given, when there are consecutive elements to replace.

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Sean de Wolski
Sean de Wolski 2015-7-20
编辑：Sean de Wolski 2015-7-20
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 2018-6-14
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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