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array that grows in size over time

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vsee
vsee on 31 Aug 2011
Is there an option to declare an array in matlab that grows as a program runs (like a vector or a list in C++)? I am trying to read a .csv file with many data points and check for each data point to meet a certain requirement and if it does initialize it to another array and keep doing so until I reach the end of the file that I read using the csvread command?Thanks for any suggestions.

Answers (1)

Fangjun Jiang
Fangjun Jiang on 31 Aug 2011
You don't need to declare it. MATLAB will automatically grow it. Although many will advise you not to do that because it slows things done, by in your case, it is really needed. For example,
>> clear a;
a=rand(3,1);
a(5)=20
a =
0.1576
0.9706
0.9572
0
20.0000
  2 Comments
Daniel Shub
Daniel Shub on 31 Aug 2011
In general no, you do not have to declare anything to start with.
b(5) = 20
works just fine. That said, there can be a substantial performance hit (especially for versions before r2011a) of not initiating the size beforehand. If the maximum size is reasonable, you can trim afterwards:
c = nan(1000, 1); % Initialize to the maximum size
% Some code that loops
c = c(~isnan); % Trim the unused slots

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