Is there a Matlab conditional IF operator that can be placed INLINE like VBA's IIF

Question

In VBA I can do the following:

A = B + IIF(C>0, C, 0)

so that if C>0 I get A=B+C and C<=0 I get A=B

Is there an operator or function that will let me do these conditionals inline in MATLAB code?

Solution 1

There is no ternary operator in Matlab. You can, of course, write a function that would do it. For example, the following function works as iif with n-d input for the condition, and with numbers and cells for the outcomes a and b:

function out = iif(cond,a,b)
%IIF implements a ternary operator

% pre-assign out
out = repmat(b,size(cond));

out(cond) = a;

---

For a more advanced solution, there's a way to create an inline function that can even do elseif, as outlined in this blog post about anonymous function shenanigans:

iif  = @(varargin) varargin{2*find([varargin{1:2:end}], 1, 'first')}();

You use this function as

iif(condition_1,value_1,...,true,value_final)

where you replace the dots with any number of additional condition/value pairs.

The way this works is that it picks among the values the first one whose condition is true. 2*find(),1,'first') provides the index into the value arguments.

Solution 2

How about simply using the fact that MATLAB automatically converts variable types when required by the operation? E.g., logical to double.

If your variables are scalar double, your code, I believe, can be replaced by

a = b + (c > 0) * c;

In this case, the operator (c > 0) values 1 (logical type) whenever c > 0 and values to 0 otherwise.

Solution 3

Others have said already that there is no ternary ?: operator in Matlab. As a solution I suggest this function, which takes three functions instead of values. Therefore the amount of unnecessary calculations is minimized and you can check conditions before starting calculations, e.g. if a value is really numeric, or finite, or nonzero:

function [ out ] = iif( condition, thenF, elseF, in, out)
%iif Implements the ternary ?: operator
%   out = iif (@condition, @thenF, @elseF, in[, out])
%
%   The result is equivalent to:
%   condition(x) ? thenF(x) : elseF(x)
%
%   The optional argument out serves as a template, if the output type is
%   different from the input type, e.g. for mapping arrays to cells and
%   vice versa.
%
% This code is in the public domain.

mask = condition(in);
if nargin <= 4
  out = in;
end

if sum(mask)
  out(mask)  = thenF(in(mask));
end
if sum(~mask)
  out(~mask) = elseF(in(~mask));
end

end

Use it like this:

f = @(y)(iif(@(x)(x > 3), @(x)(x.^2), @(x)(x/2), y))
f(linspace(0,6,10))

Solution 4

There is no built-in solution for this, but you can write an IIF yourself.

function result=iif(cond, t, f)
%IIF - Conditional function that returns T or F, depending of condition COND
%
%  Detailed 
%     Conditional matrix or scalar double function that returns a matrix
%     of same size than COND, with T or F depending of COND boolean evaluation
%     if T or/and F has the same dimensions than COND, it uses the corresponding 
%     element in the assignment
%     if COND is scalar, returns T or F in according with COND evaluation, 
%     even if T or F is matrices like char array.
%
%  Syntax
%    Result = iif(COND, T, F)
%           COND - Matrix or scalar condition
%           T  - expression if COND is true
%           F  - expression if COND is false
%           Result - Matrix or scalar of same dimensions than COND, containing
%                    T if COND element is true or F if COND element is false.
%
if isscalar(cond) 
   if cond 
       result = t;
   else
       result = f;
   end
else
  result = (cond).*t + (~cond).*f;
end  
end

Solution 5

Inspired by Jonas' answer the function below also works for mixed type input and chars, for which his function isn't stable.

function out = iif(cond, a, b)
%IIF implements a ternary operator

    % Use cell output for either char or mixed type input
    if ischar(a) || ischar(b) || ~strcmp(class(a), class(b))
        out = cell(size(cond));
        [out{cond}] = deal(a);
        [out{~cond}] = deal(b);
    else
        % Use array output and logical indexing
        out = repmat(b, size(cond));
        out(cond) = a;
    end
end

Edit: weeded out the extra conditional options in the cell branch, which were apparently remnants of a previous mistake, this is probably faster, and definitely cleaner.

View more solutions

Comments

[Tim Williams]

possible duplicate of Matlab conditional assignment

[Lance Roberts]

@Tim Williams, No, I'm looking for INLINE.

[Jonas]

Have a look at this blog post that shows how to create an inline function for iff

[Lance Roberts]

@Jonas, that worked great if you want to write up an answer with the link and an excerpt of the basics I'll upvote and accept it.

[Jonas]

@LanceRoberts: I have created the answer

[Sanjay Manohar]

For an extension of @Alex's answer, see stackoverflow.com/a/15870464/93910

[Jonas]

@EitanT: Yes, this works indeed well when you can multiply (though you may want to use parentheses around ~cond). However, the other answer already mentioned it, so I though I'd not repeat the other answer.

[masterxilo]

This is the best approximation to a C ?: which will not evaluate the branch that is not taken. Unfortunately the syntax is meh.

[Wauzl]

You could even use this do define iif = @(c,t,f) c.*(t-f) + f, so you can even do things vectorised. I think your answer is the best MATLAB-solution for simple uses.

[Ben Voigt]

Vector version doesn't handle NaN properly

[Cris Luengo]

This does not answer the question. Please take the tour before contributing to this site. Thanks!

[Cris Luengo]

The first method works only in Octave, it is not legal MATLAB syntax.

[vitaminace33]

It is. Here an official example: Content Indexing with Curly Braces, {}. mathworks.com/help/matlab/matlab_prog/…

[Cris Luengo]

You can do tern = {F,T}; tern = tern{bool+1}, but you can’t do tern = {F,T}{bool+1}.

[vitaminace33]

I see, I stand corrected. I will edit the answer to incorporate this.