如何优雅地忽略MATLAB函数的一些返回值？ [英] How to elegantly ignore some return values of a MATLAB function?

问题描述

是否有可能从函数中获得'nth'返回值，而不必为之前的所有 n-1 返回值创建虚拟变量？

比方说，我在MATLAB中有以下函数：

pre $函数[a， b，c，d] = func（）
a = 1;
b = 2;
c = 3;
d = 4;

现在假设，我只对第三个​​返回值感兴趣。这可以通过创建一个虚拟变量来实现：

  [dummy，dummy，variableThatIWillUse，dummy] = func; 
清除虚拟; 
  

但我认为这很丑陋。我认为你可以做以下事情之一，但是你不能：

[_，_， variableThatIWillUse，_] = func;

[，，variableThatIWillUse，] = func;

variableThatIWillUse = func（3）;

variableThatIWillUse = func（）（3）;

有没有优雅的做这个工作吗？

---

到目前为止，最好的解决方案是简单地使用 variableThatIWillUse 作为虚拟变量。这使我不必创建一个真正的虚拟变量来污染工作空间（或者我需要清除）。简而言之：解决方案是对每个返回值使用 variableThatIWillUse ，直到有趣的一个。返回值可以简单地忽略：

  [variableThatIWillUse，variableThatIWillUse，variableThatIWillUse] = func; 
  

我仍然认为这是非常难看的代码，但如果没有更好的方法，那么我猜我'b $ b

解决方案

这有点破解，但它有效：

首先是一个简单的示例函数：

  Func3 = @（）deal（1,2,3）; 
 [a，b，c] = Func3（）; 
％产生a = 1，b = 2，c = 3 
  

如果您在多表达式赋值的左侧使用两次变量，则较早的赋值将被后面的赋值破坏：

 并[b，b，C] = FUNC3（）; 
％yield b = 2，c = 3 
 
 [c，c，c] = Func3（）; 
％yield c = 3 
  

（编辑：只是为了检查，我也证实了这一点技巧适用于 [mu，mu，mu] = polyfit（x，y，n）如果您只关心 polyfit c>是第三个参数）

---

编辑：有更好的方法;请参阅 ManWithSleeve的回答。

Is it possible to get the 'nth' return value from a function without having to create dummy variables for all n-1 return values before it?

Let's say, I have the following function in MATLAB:

function [a,b,c,d] = func()
a = 1;
b = 2;
c = 3;
d = 4;

Now suppose, I'm only interested in the third return value. This can be accomplished by creating one dummy variable:

[dummy, dummy, variableThatIWillUse, dummy] = func;
clear dummy;

But I think this is kind of ugly. I would think that you might be able to do something like one of the following things, but you can't:

[_, _, variableThatIWillUse, _] = func;

[, , variableThatIWillUse, ] = func;

variableThatIWillUse = func(3);

variableThatIWillUse = func()(3);

Are there any elegant ways to do this that do work?

---

So far, the best solution is to simply use the variableThatIWillUse as a dummy variable. This saves me from having to create a real dummy variable that pollutes the work-space (or that I would need to clear). In short: the solution is to use the variableThatIWillUse for every return value up until the interesting one. Return values after can simply be ignored:

[variableThatIWillUse, variableThatIWillUse, variableThatIWillUse] = func;

I still think this is very ugly code, but if there is no better way, then I guess I'll accept the answer.

解决方案

This is somewhat of a hack but it works:

First a quick example function:

Func3 = @() deal(1,2,3);
[a,b,c]=Func3();
% yields a=1, b=2, c=3

Now the key here is that if you use an variable twice in the left hand side of a multiple-expression assignment, an earlier assignment is clobbered by the later assignment:

[b,b,c]=Func3();
% yields b=2, c=3

[c,c,c]=Func3();
% yields c=3

(edit: just to check, I also verified that this technique works with [mu,mu,mu]=polyfit(x,y,n) if all you care about from polyfit is the 3rd argument)

---

edit: there's a better approach; see ManWithSleeve's answer instead.

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