Error message "Index exceeds the number of array elements. Index must not exceed 3"

I have a vector of length 16384 in a cell. In some parts of my code I need up to half length, but I got an error message "Index exceeds the number of array elements." The index must not exceed 3".

Assume fsp is a 16384-length vector or length(fsp)=16384.

sp{1,1}=fsp(1:length(fsp{1,1})/2);

The above syntax looks correct, but unfortunately the result is "Index exceeds the number of array elements." "Index must not exceed 3"..

Answer 1

[Voss]

fsp is the cell array, and fsp{1,1} is the vector contained in the first element (first cell) of fsp.

You are taking the length of the vector fsp{1,1}, divided by 2, which is 8192, and using that to try to index into the cell array fsp, which apparently has 3 elements (three cells).

If you want sp{1,1} to contain the first half of the vector fsp{1,1}, do this:

sp{1,1} = fsp{1,1}(1:numel(fsp{1,1})/2);

where I've used numel instead of length for clarity, but that does not affect the behavior if fsp{1,1} is a vector.

Or more simply:

sp{1,1} = fsp{1,1}(1:end/2);

Also, in case the vector fsp{1,1} had an odd number of elements, the above would give you a warning since numel(fsp{1,1})/2 (or length(fsp{1,1})/2) would not be an integer, so to handle that case as well, you could do:

sp{1,1} = fsp{1,1}(1:floor(end/2)); % don't include the middle element in case there's an odd number of elements

or:

sp{1,1} = fsp{1,1}(1:ceil(end/2)) % do include the middle element in case there's an odd number of elements

depending on how you want it to work.

A concrete example:

fsp = {1:7};
fsp{1,1}(1:end/2)

Warning: Integer operands are required for colon operator when used as index.

ans = 1×3

1 2 3

fsp{1,1}(1:floor(end/2))

ans = 1×3

1 2 3

fsp{1,1}(1:ceil(end/2))

ans = 1×4

1 2 3 4

[Teshome Kumsa]

Thank you! Perfect!

[Voss]

You're welcome!

If that works for what you're intending to do and it makes sense, please click 'Accept This Answer'. Otherwise, let me know if you have any questions. Thanks!

[Teshome Kumsa]

I have accepted it. Thanks!

[Voss]

I appreciate it!