# Index slice of ND array of unknown dimension

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Evan on 12 Jun 2017
Edited: Stephen23 on 26 Mar 2020
Let's say I have a 3D array A, and I want to remove a slice:
A(i,:,:) = [];
But what if I don't know the dimension of the array beforehand? Just doing
A(i,:) = [];
Is valid, but reshapes the array into a 2D matrix.
I was thinking something like:
A(i,indices{:}) = [];
but I don't think you can put a colon operator in a cell.

Stephen23 on 12 Jun 2017
Edited: Stephen23 on 12 Jun 2017
If you do not know the size of the array before hand then you can call subsasgn directly. The function subsasgn is the actual function that MATLAB calls whenever you assign to an array using the indexing convenience operators () or {}, e.g. X(1) = 2, in just the same way that 1+2 is just a convenience operator for plus(1,2). We can also call subasgn directly, just like we could call plus if we so wished.
Here is a simple example of removing one row of A without hard-coding how many dimensions it has:
>> A = rand(5,4,3,2);
>> S.subs = repmat({':'},1,ndims(A));
>> S.subs{1} = 3; % the third row
>> S.type = '()';
>> B = subsasgn(A,S,[]);
>> size(B)
ans =
4 4 3 2
Daniel Plotnick on 23 Mar 2020
It looks like this has changed in more recent updates: I had been using this technique, but it failed when using it on a gpuArray. The included code below now works for gpuArrays and normal arrays:
A = gpuArray.rand(5,4,3,2);
v = repmat({':'},ndims(A),1);
v{1} = 3; % Do the third row
B = A;
B(v{:}) = []; % Note, you can replace this with a numeric to substitite instead of delete
size(B)
Stephen23 on 26 Mar 2020
Edited: Stephen23 on 26 Mar 2020
@Daniel Plotnick: you should put that as an Answer, so other users could vote for it.

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