# Reaching the element of an array passed to a function

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Hsin-Hua Wang on 4 Mar 2017
Commented: Hsin-Hua Wang on 7 Mar 2017
I'm trying to create a function y=f(x) composed of two different parts for x < constant C & x >= C. When one pass an array A to f(x), the return would be an array B where Bij=f(Aij) How do I create a valid "if statement" in the function f? Below is the code I'm using (say I want to create a step function) What happened is since A is an array, all statement would be false Is there a way to call the "current" element in array A?
function y=f(A)
if A >= C
y=0
elseif A<C
y=1
end
end

Sky Sartorius on 4 Mar 2017
The first step needs to be to find the indices of the array that correspond to the conditional statement. You can use something like find for this, but logical indexing is usually preferred.
y = ones(size(A)); % Set up y.
ind = A >= C; % First, find elements of A that are greater than C.
y(ind) = 0;
y(~ind) = 1;
The last line is not absolutely necessary in this case, since we initialized y using ones, but you could put an equation here if something more complicated was needed.

#### 1 Comment

Hsin-Hua Wang on 7 Mar 2017
Thank you! this is what I need to know, logical indexing.

Image Analyst on 4 Mar 2017
Edited: Image Analyst on 4 Mar 2017
Why not just do
B = A < C;
Why bother making a function at all when a simple one-liner will do it?
You're either over-thinking it or I'm not understanding what you want. So please post examples with x, y, A, B, and/or C so we can see what you want.

#### 1 Comment

Hsin-Hua Wang on 7 Mar 2017
I'm actually trying to make a more complex function and was just using step function as an example. Thanks still!