matlab: quick function that can produce NaN if x > 1 - matlab

Question

I am looking for a one-line function f = #(x) {something} that produces NaN if x >= 1, and either 0 or 1 if x < 1.
Any suggestions?

Answer 1

Aha, I got it:
f = #(x) 0./(x<1)
yields 0 for x < 1 and NaN for x>=1.

Answer 2

Here's a modification of Jason's solution that works for arrays. Note that recent versions of MATLAB do not throw divide-by-zero warnings.
>> f = #(x) zeros(size(x)) ./ (x < 1)
f =
#(x)zeros(size(x))./(x<1)
>> f(0:.3:2)
ans =
0 0 0 0 NaN NaN NaN
Update: a coworker pointed out to me that Jason's original answer works just fine for arrays.
>> f = #(x) 0./(x<1)
f =
#(x)0./(x<1)
>> f(0:.3:2)
ans =
0 0 0 0 NaN NaN NaN

Answer 3

Here's a less obvious solution (vectorized nonetheless):
f = #(x) subsasgn(zeros(size(x)), struct('type','()','subs',{{x>=1}}), nan) + 0
Basically its equivalent to:
function v = f(x)
v = zeros(size(x));
v( x>=1 ) = nan;
The +0 at the end is to always force an output, even if f called with no output arguments (returned in ans). Example:
>> f(-2:2)
ans =
0 0 0 NaN NaN

Answer 4

Here's a solution that won't risk throwing any divide-by-zero warnings, since it doesn't involve any division (just the functions ONES and NAN):
f = #(x) [ones(x < 1) nan(x >= 1)];
EDIT: The above solution is made for scalar inputs. If a vectorized solution is needed (which isn't 100% clear from the question) then you could modify f like so:
f = #(x) arrayfun(#(y) [ones(y < 1) nan(y >= 1)],x);
Or apply ARRAYFUN when calling the first version of the function f:
y = arrayfun(f,x);