How can I add elements to pre-allocated array?

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Erik Hricka 2018-3-9

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https://ww2.mathworks.cn/matlabcentral/answers/387336-how-can-i-add-elements-to-pre-allocated-array

评论： Stephen23 2018-3-9

 I used "Data = zeros(1,100);" but I want to replace zeros with values in cycle like this:
for i = 1 : 10
   var1 = "somefunctionthatgives(1,10)vector"
   Data = [Data,var1];
end

Without allocation is runs just perfectly but MATLAB keeps suggesting to pre-allocate array for speed... I would normally ignore it but I have to solve task in which at the end variable Data would be vector (1,10000000). And doing it in minimum time is also part of the task. Can somebody help me?

Thanks a lot...

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Von Duesenberg 2018-3-9

Just a hint in pseudo-code : Data(1:10) = var1

Stephen23 2018-3-9

"MATLAB keeps suggesting to pre-allocate array for speed..."

Always write code using good code practices.

When someone writes code only using inefficient/buggy practices, then they will learn and practice only those methods. And then when one day it becomes critical to write something better, they will have no experience or idea how to write efficient code.

Writing preallocated code also means that the code is more generalized, so that even if it was tested with ten elements it will work happily with ten million. Why limit the code for no reason?

"I would normally ignore it"

Never ignore the hints from the editor.

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Answer 1

Von Duesenberg 2018-3-9

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在 MATLAB Online 中打开

Try this:

Data = zeros(100,1);
i = 1;
while i < length(Data)
    var1 = randperm(10);
    currentIdx = (0:9)+i;
    Data(currentIdx) = var1;
    i = i + 10;
end