Michael asked . 2023-11-28

Find function misbehaves when Indexing into array

I have a function which searches an array for the first value which is below a given tolerance. First, it creates a logic array using the input and a "less than" condition. Then it finds the index of the first instance of "True" in the LogicArray using the find function. If no "True" value could be found, it sets the index to be the last value in the array (in this case, 125). Then it uses the found index value to return a corresponding array value. 

function [FindIndex, RxComplete] = IndexCheck(x,y)
Tolerance = 100;
LogicArray = x < Tolerance;
FindIndex = find(LogicArray,1,'first');
if isempty(FindIndex)
    FindIndex = 125;
end
RxComplete = y(FindIndex,1);
end

The function is then applied to a cell array using cellfun.

[Index_output, Array_output] = cellfun(@IndexCheck, x, y, 'UniformOutput',false);

The code works for the above application, but it mesbehaves when I try to only search certain elements of my input array. For example, I want the function to skip the first 5 elements of the array so I index into LogicArray with (5:end). This should tell the find function to only start searching for a "True" after the first 5 elements.

function [FindIndex, RxComplete] = IndexCheck(x,y)
Tolerance = 100;
LogicArray = x < Tolerance;
FindIndex = find(LogicArray(5:end),1,'first');
if isempty(FindIndex)
    FindIndex = 125;
end
RxComplete = y(FindIndex,1);
end

find , indexing , cell array , MATLAB , Language Fundamentals