Defining anonymous function using an "if" statement

Question

John 2015-1-5

2
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/168998-defining-anonymous-function-using-an-if-statement

评论： Oscar Raya i Casanova 2020-1-29

I'm trying to define an anonymous function using an "if" statement. Here is a minimum "not working" example (my code is more convoluted, but this illustrates the issue):

clc;
clear all;
f=@(x)x^2;
g=@(x) x;
if f(x)>=g(x)
    h=@(x) f(x)
else h=@(x) g(x)
end

The point is that I don't want to create an m file and have to recompute both f and g in it (my actual problem would require recomputing many more). So the question is:

1-) Is it possible to create an anonymous function using "if" statements (fixing the code above)?

2-) Is it possible to define function h on a separate m file, without having to recompute f and g inside of it?

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Matt J 2015-1-5

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/168998-defining-anonymous-function-using-an-if-statement#answer_164069

在 MATLAB Online 中打开

You can also do things like the following

f=@(x)x^2;
g=@(x) x;
h=@(x) fg_mfile(x,f,g);
 function out=fg_mfile(x,f,g)  %put this in mfile
    fval=f(x);
    gval=g(x);
        if fval>=gval
          out=fval;
        else 
          out= gval;
        end
   end

2 个评论
显示无隐藏无

yang 2018-8-24

you can do like this h=@(x)max(f(x),g(x))

Matt J 2018-8-24

编辑：Matt J 2018-8-24

In this particular example, that is true. More complicated h() might require an mfile to express, however.

请先登录，再进行评论。

Answer 2

Roger Stafford 2015-1-5

4
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/168998-defining-anonymous-function-using-an-if-statement#answer_164067

在 MATLAB Online 中打开

Try this:

f = @(x) (x.^2>=x).*x.^2+(x.^2<x).*x

5 个评论
显示 3更早的评论隐藏 3更早的评论

John 2015-1-6

I see. I checked the references you provided and now I understand.

Alec Jacobson 2016-12-16

在 MATLAB Online 中打开

This style/hack has two (more) "gotchas".

1) Suppose L(x) is true, but g(x) produces nan/inf. Then h(x) = nan rather than f(x).

2) Suppose L(x) is true and g(x) is very expressive to compute or has side-effects (admittedly rare for matlab code), g(x) will still be called. This is very different behavior from:

if L(x)
  return f(x)
else
  return g(x)

I really wish matlab had full-citizen anonymous functions...

请先登录，再进行评论。

Answer 3

Cristobal Montecino 2019-6-26

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/168998-defining-anonymous-function-using-an-if-statement#answer_380937

编辑：Cristobal Montecino 2019-6-26

在 MATLAB Online 中打开

I use:

call = @(fun) fun();
cellget = @(cell, index) cell{index};
iff = @(test, truefn, falsefn) call(cellget({falsefn, truefn}, test + 1));

And:

arrayget = @(arr, index) arr(index);
ifv = @(test, trueval, falseval) arrayget([falseval, trueval], test + 1);
%or
cellget = @(cell, index) cell{index};
ifv = @(test, trueval, falseval) cellget({falseval, trueval}, test + 1);

Examples:

iff(true, @() 2, @() this_throw_an_error)
% out: 2
iff(false, @() 2, @() this_throw_an_error)
% out: Undefined function or variable 'this_throw_an_error'.
ifv(true, 2, 3)
% out: 2
ifv(true, 2, this_throw_an_error)
% out: Undefined function or variable 'this_throw_an_error'.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Oscar Raya i Casanova 2020-1-29

在 MATLAB Online 中打开

Nice tip. As improvement for the first option:

call = @(fun,par) fun(par{:});
cellget = @(cell, index) cell{index};
iff = @(test, truefn, falsefn, truePar, falsePar) call( ...
    cellget({falsefn, truefn}, test + 1), ... % functions
    cellget({falsePar, truePar}, test + 1) ... % params
);

Examples:

f1 = @(a,b) a + b;
f2 = @(a,b,c) a*b + c;
f3 = @() 7;
iff(true,f1,f2,{1,2},{1,2,3});
% out: 3
iff(false,f1,f2,{1,2},{1,2,3});
% out: 5
iff(false,f1,f3,{1,2},{});
% out: 7