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How can I read the elements of an array backwards?

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I have an array with x = 250000 elements. I want the code to read backwards a part of it:
k = pks3(1):-1:1;
%read data points backwards starting from pks3 and ending at the beginning
So even though I have i = 10 pks3 peak points, I want to create an array k from the first point pks3(1). But, the problem is that in the end I get k = 255997855 elements, in which the pks3 point for example is repeated for several hundreds of times. The rest of the code is this:
k = pks3(1):-1:1;
%read data points backwards starting from pks3 ending to pks3 again.
first = k(k<xfb1); % find all k such that k is smaller than xfb1
if ~isempty(first)
first = first(1); %store the first number which is smaller than xfb1
disp('No value of k is smaller than xfb1.')
distQ = length(first:pks3(1));
Qstart = locs_RwaveB(1)*distQ; %distance from locs_RwaveB to Qstart point
What am I doing wrong?

Accepted Answer

Ahmet Cecen
Ahmet Cecen on 18 May 2016
It appears to me that you are trying to do something very simple in a very convoluted way, probably due to programming practices in another language.
If you need to read x in reverse order, assuming x is a column vector simply do:
x = flipud(x); % flips the vector.
And now you can access it in forward order.
Stephen23 on 18 May 2016
The problem is not the end, it is the pks3(1). What value does pks3(1) have?

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More Answers (1)

Johannes Kalliauer
Johannes Kalliauer on 19 Apr 2021
a horizontal vector can be fliped using fliplr

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