How to define several variables from vector at the same time
166 vues (au cours des 30 derniers jours)
Afficher commentaires plus anciens
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
0 commentaires
Réponse acceptée
Jan
le 11 Oct 2017
Modifié(e) : Jan
le 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 commentaires
Jan
le 12 Oct 2017
Modifié(e) : Jan
le 12 Oct 2017
@Martin: This is a completely different question. The solution is easy:
function [xf, yf] = Cycle(fluid, massflow)
... calculate x and y
xf = x(end);
yf = y(end);
end
as you have mentioned in your question already. This is clean, clear and fast. Searching for more complicated methods like deal() is a waste of time - for programming and for the processing.
Remember Donald Knuth's mantra:
KISS - Keep it simple stupid
Perhaps the bigger problem is that you have 17 vectors in your code. Would a matrix or a cell array be smarter? Then the extraction of the last element could be done in a loop or by a simple indexing. Returning a vector instead of a bunch of variables might be an option also.
Bill Tubbs
le 3 Fév 2020
Modifié(e) : Bill Tubbs
le 3 Fév 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.
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?
Plus de réponses (2)
Voir également
Catégories
En savoir plus sur Entering Commands dans Help Center et File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!