Access a single element of an anonymous function that returns an array

I have an anonymous function that returns an array. I'd like to be able to create a new anonymous function that consists of a single element of this array WITHOUT using matlabfunction (which is infuriatingly restrictive in several respects).

For example, consider the following code (it's a ridiculously simple example, for expository purposes, obviously there are easy ways of dealing with this example, but my real problem is more complex)

y = sym('y',[1,4])
 f = @(y)[y(1);y(2);y(3);y(4)]
 f(y)

which returns

ans =
 y1
 y2
 y3
 y4

I'd now like to define a new anonymous function which extracts, say, the third element of this array. Obviously,

g    = @(y) f(y)(3)

won't work. Is there some way to accomplish this? Again, solns involving matlabfunction are not satisfactory.

Any suggestions would be most appreciated!

Leo

Answer 1

[Walter Roberson]

indexat = @(expr, index) expr(index);

g = @(y) indexat(f(y), 3);

[Leo Simon]

Fabulous, thanks very much Walter, works beautifully

[Stephen23]

"could you please explain what you mean by "expr" and "index"? "

They are the input arguments of an anonymous function:

https://www.mathworks.com/help/matlab/matlab_prog/anonymous-functions.html

Answer 2

[Lauren Barr]

This is really helpful, thank you! I was wondering if there is a way to extend it, so that I can index one particular value in a 2D matrix, instead of indexing into a vector?

For example, this doesn't seem to work:

indexat = @(expr, index) expr(index);

g = @(y) indexat(f(y), (1,3));

But maybe I am missing something obvious.

Thank you!

Lauren

[Lauren Barr]

I think I found the answer here!

https://uk.mathworks.com/matlabcentral/answers/248921-how-to-select-element-of-matrix-that-is-created-with-function-handle

[Stephen23]

You can create a general solution for any number of dimensions:

indexat = @(expr, varargin) expr(varargin{:});