Creating a new variable in each iteration...
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I want to create a new variable in each iteration of a for loop... x_1, x_2, x_3, etc... up to x_50
count = 0;
for i = 2:2:100
count = count + 1;
x_(...I want "count" to go in here... what is the code to achieve this?...) = i^2
end
Basically, there should be an x_1 = 4 created in the first iteration, x_2 = 16 in the second iteration, etc... up to x_50 = 10000
Thanks
D Howard
Note: I have seen others ask similar questions, with experienced users saying things like "this is a bad idea because it is hard to reference these later..." and they suggest creating a vector, but my problem is more general and this is not an option.
采纳的回答
James Tursa
2012-2-20
E.g., with the usual caveats about this typically being a bad idea:
eval(['x_' num2str(count) ' = i^2']);
11 个评论
James Tursa
2012-2-20
P.S. I would be curious to know why using a vector or cell array is not a viable option for you.
Doron
2012-2-20
Jiro Doke
2012-2-20
If each loop creates a matrix, then you can still use "cell arrays" or "structures"
Doron
2012-2-20
Jiro Doke
2012-2-20
The FAQ link that Walter referenced is a good one. There are a number of reasons, but I like the readability and performance.
for i = 1:100
A{i} = i^2
end
is so much easier to read and understand than
for i = 1:100
eval(['x_' num2str(i) ' = i^2;']);
end
It also depends on what you want to do with the data afterwards. For example, I may need to access the data for analysis or plotting:
for i = 1:100
doSomeAnalysisAndPlot(A{i});
end
Which is again easier to understand than
for i = 1:100
doSomeAnalysisAndPlot(eval(['x_' num2str(i)]));
end
Finally, there's a bunch of optimization going on with MATLAB to make things run faster. Calling your data as "A{i}" is faster than "eval(['x_' num2str(i)])". It may not be an issue with your particular data size, but if you start working with large data in the future, you'll regret it if you keep using "eval" like that. So my argument is why not learn it the recommended way if it doesn't hurt you now but may help you *a lot* in the future.
Doron
2012-2-20
Doron
2012-2-20
Jiro Doke
2012-2-20
Great!
I'm not sure I understand the question. The nice thing about using a cell array is that you'll only have one variable. You name it whatever you like, e.g. "myData". Each individual components are simply stored/accessed by using the index number, i.e. you don't name it.
Then if you want to see the contents of the 8th component, you just refer to it as "myData{8}"
Does that make sense?
Doron
2012-2-20
Jiro Doke
2012-2-20
Oh I see. Right, you don't want to do that. If you have P already and want to break it up, you should create a different cell array with a different name. Actually, it probably won't let you create it and give you an error.
You may also want to take a look at the function "mat2cell", that allows you to take a regular matrix P and convert to a cell array.
Doron
2012-2-20
更多回答（1 个）
Walter Roberson
2012-2-20
2 个投票
As best I recall at the moment, I have not had a need for dynamic variable names since the days I programmed in REXX ... 25 years ago.
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