Breaking down a large array

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Senaasa
Senaasa on 23 May 2013
Hi,
I have a large array (nx1) of values that I'd like to break up into a new array. This new array takes the first 200 or so values from the original array and then only selects every 3rd value (or even a logarithmic selection) of the original array to construct the new array. I was thinking about doing this with a loop, but I was wondering if matlab had any built-in functions that could do this.
Thanks, Charles

Accepted Answer

Roger Stafford
Roger Stafford on 23 May 2013
For spacing every third element
p = a:3:b;
For logarithmic spacing
p = round(k*a.^(1:n));
for appropriate a, k, and n. Then do this:
new_array = old_array(p);
  4 Comments
Cedric
Cedric on 23 May 2013
Edited: Cedric on 23 May 2013
What Roger is generating is an array of IDs/positions (that he then uses for indexing operations); you can work with these as you work with any other array; in particular, you can concatenate them, e.g.
p = [1:200, 203:3:1000] ;
or
p = [1:200, 200+3^(1:5)] ;
etc. Experiment with smaller numbers so you can easily visualize p.
Senaasa
Senaasa on 23 May 2013
Ok, I've got it now. Thanks a lot guys

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