How to obtain a subset of functions from a function handle that is a vector of functions in Matlab

问题

In Matlab, I have a function handle defined as a vector like this

F = @(x) [... 
coeff1*x(1)*x(4); ...
coeff2*x(3); ... 
coeff3*x(7)*x(3) ...
];

In reality it has 150 rows. I need to extract different subsets the functions in the rows. For example make a new handle from the rows 3:17 of those in F. But I can't just go indexing a handle. Is there a solution?

Edit: I need the subset as a new handle, in other words I can not evaluate the entire F and just select the solution rows.

Thanks in advance.

回答1:

How about this:

F = @(x)[
     5*x.^2*x*4;
     6*x; 
     12*x.^2*x*3
    ];

newF = getFunHandles(F,2:3);

where getFunHandles works for any arbitrary range, e.g. 3:17

function f = getFunHandles(F, range)
funStr = textscan(func2str(F),'%s','delimiter',';');
funStr = regexprep(funStr{1}, {'@(x)[', ']'}, {'', ''});
newFunStr = strcat('@(x)[',strjoin(funStr(range),';'),']');
f = str2func(newFunStr);

回答2:

It's a bit messier to create but it might make more sense to have a vector of function handles rather than a function handle that creates a vector:

F = {... 
     @(x)coeff1*x(1)*x(4); ...
     @(x)coeff2*x(3); ... 
     @(x)coeff3*x(7)*x(3) ...
    };

And now you can call

cellfun(@(x)x(y),F(3:17))

or even

F2 = @(y)cellfun(@(x)x(y),F(3:17))

And now you can call

y = rand(10,1)
F2(y)

And only get back rows 3 to 17 of your original F. This is basically just wrapping up loops in shorthand. You need to make sure your input y has the right size or you will get an error (i.e. if y is [1,2] and your line three tries to call y(7) you will get an error)

回答3:

You can convert your original function to the format used in Dan's answer:

>> G=regexp(func2str(F), ';|\[|\]', 'split')
G = 
    '@(x)'    'coeff1*x(1)*x(4)'    'coeff2*x(3)'    'coeff3*x(7)*x(3)'    ''
>> H=cellfun(@str2func, strcat(G{1}, G(2:end-1)), 'uni', 0)
H = 
    @(x)coeff1*x(1)*x(4)    @(x)coeff2*x(3)    @(x)coeff3*x(7)*x(3)

Now H is a cell array containing the function handles and you can index into that.

来源：https://stackoverflow.com/questions/36279499/how-to-obtain-a-subset-of-functions-from-a-function-handle-that-is-a-vector-of-f

标签

matlab

function

indexing

handle