MATLAB: “end-1” as parameter

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I have a question on MATLAB Onramp Chapter 5.1 Indexing into Arrays, Task 3:
Under what "real" scenario would I use the "end-1" command to find a value?
In the given example of MATLAB Onramp, the task is to find the value in the 6th row and 3rd column. I understand that I can use the keyword "end" to either find a row or column index to reference of the last element, which is quick and straightforward in a dataset, but why would I use the "end-1" as parameter? Doesn't it make it too complicated to find an "unknown" value?
Any further explanation on this is much appreciated.

Best Answer

Well, end-1 is not an unknown location. It's the element before the last. There are plenty of scenarios where you'd want the nth element before the end, so end-n is very useful. e.g.:
  • Implementing a LIFO (Last In First Out) stack. When you want to pop the last element from the stack:
function [stack, element] = pop(stack)
   element = stack(end);      %get last element
   stack = stack(1:end-1);  %return the stack without the last element
end
  • When you want to remove the border around an image:
function croppedimage = cropborder(sourceimage, bordersize)
   croppedimage = sourceimage(bordersize+1:end-bordersize, bordersize+1:end-bordersize, :);
end
  • split a vector into two:
function [firsthalf, secondhalf] = splitmiddle(vector)
    firsthalf = vector(1:ceil(end/2));
    secondhalf = vector(ceil(end/2)+1:end);
end
  • etc.
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