Change variable name in a loop

Question

Yoshihiro 2012-6-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/40287-change-variable-name-in-a-loop

编辑： Stephen23 2022-11-23

Hi,

I have a problem with naming a variable during a for loop. I want to change the variable name in each iteration, so I use eval function for naming like this

dataset=rand(3);

for i=1:N

eval(['NAME_' num2str(i) '=dataset']);

end

But with eval function I always have out put on command window. Does anyone knows better solution for naming or not to show the output of eval function?

Thanks,

2 个评论
显示无隐藏无

Stephen23 2018-6-28

编辑：Stephen23 2018-6-28

@Rachael Brimhall: here is a resource you might find useful:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

JAMES WAITE 2019-4-11

@Stephen Brimhall: found your resource helpfull for my issue. Thanks!

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2012-6-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/40287-change-variable-name-in-a-loop#answer_49909

http://matlab.wikia.com/wiki/FAQ#How_can_I_create_variables_A1.2C_A2.2C....2CA10_in_a_loop.3F

2 个评论
显示无隐藏无

Joseph Cheng 2014-9-4

编辑：Joseph Cheng 2014-9-4

在 MATLAB Online 中打开

In addition to Walter's post you could go:

dataset=rand(3);

for i=1:N
     Name{i} =dataset;
end

Which is equivalent to your Name_# variable. Instead of working with Name_# you would type Name{#} instead. Note the {} bracket type as these are cells. Using cells also give the ability to have different sizes of dataset. Also with the Name{#} convention you do not have to hard code or use eval again to reprocess the data. For instance if there needs to be a scaling of all the data in Name you would have to hard code Name_1*2, Name_2*2, etc. you could write a for loop to do it and without using eval.

Byron Uzoka 2020-7-11

🤔

请先登录，再进行评论。

Answer 2

Sirshendu Mondal 2020-5-4

4
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/40287-change-variable-name-in-a-loop#answer_430185

Instead of

eval(['NAME_' num2str(i) '=dataset']);

use

eval(['NAME_' num2str(i) '=dataset;']);

5 个评论
显示 3更早的评论隐藏 3更早的评论

Stephen23 2020-7-11

编辑：Stephen23 2020-7-11

"However, this is going to creat a single cell of very big size (maybe)."

Not unless you have millions of tiny numeric arrays (in which case they should probably be stored in one numeric array anyway). The cell array itself is just a header of links to other data arrays, so really the cell array just adds a tiny overhead, either 60 bytes (for 32 bit OS) or about 112 bytes (for 64 bit OS) per cell, as the documentation explains:

https://www.mathworks.com/help/matlab/matlab_prog/memory-allocation.html#brh72ex-18

On top of that is the circa 104 bytes of meta-data that every MATLAB array has. The overhead and the fact that the contents of cell arrays are not stored in contiguous memory is also explained in the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/strategies-for-efficient-use-of-memory.html.

Because the contents of the cell array are not stored contiguously it really makes very little difference to memory consumption, because they are allocated memory in much the same way as separate arrays are (because they are separate arrays).

"I have experinced that during image processing."

Images tend to be moderately large arrays, and it is common that not all images in a data set can be loaded into memory simultaneously. Because the image size (e.g. millions of bytes) is likely to be much larger than the cell array header (a few hundred bytes) then storing the arrays separately vs. in a cell array won't make much difference at all.

David Valentine 2022-11-22

Thank you so much for this anwer(and the querier for that matter)! I'm working on a project that needed something like this, and all I could find was people saying to make either a structure or double array.

Stephen23 2022-11-23

编辑：Stephen23 2022-11-23

"...all I could find was people saying to make either a structure or double array."

You can't have done very much reading on this topic if that was "all" the advice you found.

The advice given on this forum is much more nuanced and situation specific:

https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval

请先登录，再进行评论。

Change variable name in a loop

2 个评论
显示无隐藏无

采纳的回答

2 个评论
显示无隐藏无

更多回答（1 个）

5 个评论
显示 3更早的评论隐藏 3更早的评论

另请参阅

类别

标签

Community Treasure Hunt

Change variable name in a loop

2 个评论 显示 无隐藏 无

采纳的回答

2 个评论 显示 无隐藏 无

更多回答（1 个）

5 个评论 显示 3更早的评论隐藏 3更早的评论

另请参阅

类别

标签

Community Treasure Hunt

2 个评论
显示无隐藏无

2 个评论
显示无隐藏无

5 个评论
显示 3更早的评论隐藏 3更早的评论