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How to define several variables from vector at the same time

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Martin Olafsen
Martin Olafsen on 11 Oct 2017
Edited: Bill Tubbs on 3 Feb 2020
Hi
I am trying to define several variables at the same time. The data for each variable is saved in a vector. I have tried the following:
x = [1 2 3];
y = [4 7 9];
[a b] = [x(end) y(end)]
%Or alternatively
[c d e] = [x(1) x(2) x(3)]
When I try this I receive the "Too many output arguments." error. Is there some easy way to do this?
I realize I could use:
a = x(end)
b = y(end)
But I would like a cleaner method.
Regards

Accepted Answer

Jan
Jan on 11 Oct 2017
Edited: Jan on 11 Oct 2017
[a, b, c] = deal(x(1), x(2), x(3))
I am not sure that this is "cleaner", if you do this for many variables. It is slightly slower than the direct and simple:
a = x(1);
b = x(2);
c = x(3);
deal and num2cell have a certain overhead. The code might be more compact, if you do this in one line instead of 3, but internally much more code lines are processed. I'm convinced, that the code will not suffer from additional lines, if they are such simple and clear: neither a human reader nor the Matlab interpreter will have any problems with them. Do not try to optimize the optical appearance of the code. It is more valuable to keep the code fast (to optimize the run time) and simple (to optimize the time for debugging and maintaining).
  3 Comments
Bill Tubbs
Bill Tubbs on 3 Feb 2020
From the title, I thought this would answer my problem but it doesn't. I have a vector params and I want to extract three parameters from it.
This doesn't work:
[b1, a1, a2] = deal(params(2:4));
deal(X) copies the single input to all the requested outputs.
But why the need for any function to do this? Wouldn't it be nice and logical if this worked:
>> [b1, a1, a2] = params(2:4);
Insufficient number of outputs from right hand side of equal sign to satisfy assignment.
I see there is a note in the documentation saying:
Beginning with MATLAB® Version 7.0 software, you can access the contents of cell arrays and structure fields without using the deal function. See Example 3, below.
Why not allow it for vectors as well?

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More Answers (2)

KL
KL on 11 Oct 2017
Edited: KL on 11 Oct 2017
You can use cell arrays and get the comma separated lists,
xy = num2cell([x y])
[a b] = xy{1,[3 6]};
[c d e] = xy{1, 1:3};

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