# array manipulation - a few basic questions

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Tom il 18 Mar 2012
Hi, I have to do a bit of array manipulation and I really don't have a clue about it.
First I need to know how to take a double array, and turn it in to a 2046x1 array (twice as long), with 1024-2046 just being exactly the same as 1-1023.
Then I need to know how to chop off the first half of an array, in this case taking a 2046x1 array and disregarding the first 1-1023, leaving only a 1023x1 array made up from only the second half of the 2046x1 array.
I know it's simple stuff, but I just haven't done it before.
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Matt Fig il 2 Nov 2012
Tom's question
Hi, I have to do a bit of array manipulation and I really don't have a clue about it.
First I need to know how to take a double array, and turn it in to a 2046x1 array (twice as long), with 1024-2046 just being exactly the same as 1-1023.
Then I need to know how to chop off the first half of an array, in this case taking a 2046x1 array and disregarding the first 1-1023, leaving only a 1023x1 array made up from only the second half of the 2046x1 array.
I know it's simple stuff, but I just haven't done it before.

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### Risposta accettata

Rick Rosson il 19 Mar 2012
x = rand(1023,1);
y = repmat(x,2,1);
z = y(1024:2046);
HTH.
Rick
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Tom il 19 Mar 2012
I guessed that z = y(numel(x)+1:numel(y)); would work too. That make sense?
Rick Rosson il 19 Mar 2012
Yes, at least in this particular case, but not generally.

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