How to make empty array of specific size?

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Zeynab Mousavikhamene
编辑： HAG 2023-10-5
I used A = ClassName.empty(sz1,...,szN) or A = ClassName.empty(sizeVector) syntax :
a=ClassName.empty(2,2)
but I got this error:
Undefined variable "ClassName" or class "ClassName.empty".
  2 个评论
Walter Roberson
Walter Roberson 2019-10-14
You would have to substitute the name of the class for ClassName
Zeynab Mousavikhamene
Zeynab Mousavikhamene 2019-10-14
编辑：Zeynab Mousavikhamene 2019-10-14
@Walter Roberson I changed to a.empty(2,2). But now a=0 and isempty(a)=0. Why? It should be ''empty'', not zero

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回答（4 个）

Walter Roberson
Walter Roberson 2019-10-14
编辑：Walter Roberson 2023-4-9
Steven Lord
Steven Lord 2019-10-14
Replace ClassName with the name of the class for which you want to create the empty array.
But in order to use the empty method, the size of the array you want to create must be 0 in at least one of its dimensions. You can't, for example, have a 2-by-2 empty array. If you want to make a double 2-by-2 array, use zeros, ones, rand, eye, etc.
x = zeros(2); % 2-by-2 double array filled with 0's
y = ones(2, 'single'); % 2-by-2 single array filled with 1's
z = int8.empty(2, 2, 0) % 2-by-2-by-0 int8 array
  2 个评论
Zeynab Mousavikhamene
Zeynab Mousavikhamene 2019-10-14
@ Steven Lord Thanks but as I said in the question, for some reason I dont want to create with numbers like zero or one and it seems matlab does not have that capability.
Steven Lord
Steven Lord 2019-10-14
If the array has at least one element, those elements must have a value. Let's say you created your "empty" 2-by-2 matrix a. What specifically do you want the value of q to be after running the following line of code?
q = a(1, 1);

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Linnéa Haugen
Linnéa Haugen 2023-4-9
编辑：Linnéa Haugen 2023-4-9
I found another solution that starts out empty. i also wanted to create an empty array, with 2 columns but of unknown length.
arr = [[], []];
if ..
else
arr(end+1,1) = a;
end
if..
arr(end,2) = b;
end
a and b are changing in a for loop and i only need to save some values. i'm finding peaks and if i find one i save to location (a) and change the hight by the amount (b).
I only have an interest in the values i change, and i don't know how many i'll change in advance.
HAG
HAG 2023-10-5
编辑：HAG 2023-10-5
Ran in:
To create an empty array of any length, use zeros function
zeros(4,0)
ans = 4×0 empty double matrix

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