Is this a valid expression?

Hi

offsets = [32    48    64    80    96   112];
[X,Y,Z] = ndgrid([-1, 0, 1]);
offsetArray = [Z(:), Y(:), X(:)];
offsetArray(sum( offsetArray == [0, 0, 0], 2 ) == 3, :) = [];

I'm wondering whether below is a valid expression since I see a red tilde warning sign below the left bracket after the transpose sign in below

tmpOffsets = repmat( offsets(:), [1, size( offsetArray, 1 )] )'(:);

And the error message says

tmpOffsets = repmat( offsets(:), [1, size( offsetArray, 1 )] )'(:);

Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

What could possibly went wrong?

Answer 1

[Rik]

You can't index the output of the transpose function like that. You can either do it explicitly in multiple steps, or use the function syntax:

%option 1:
tmpOffsets = repmat( offsets(:), [1, size( offsetArray, 1 )] );
tmpOffsets = tmpOffsets';
tmpOffsets = tmpOffsets(:);

%option 2:
tmpOffsets= reshape(permute(repmat( offsets(:), [1, size( offsetArray, 1 )] ),[2 1]),[],1);

I would go for option 1, because it is much easier to see what is happening.

[Guillaume]

Note: for the record, option 3 is simpler and even easier to see what is happening:

tmpOffsets = repelem(offsets(:), size(offsetArray, 1));

should be marginally faster as well.

Answer 2

[Guillaume]

As matlab tells you is not valid, you can't have (:) on the output of a function. Since (:) is simple a reshape,

tmpOffsets = reshape(repmat( offsets(:), [1, size( offsetArray, 1 )] )', [], 1);

would work.

edit: on the other hand, the above is simply:

tmpOffsets = repelem(offsets(:), size(offsetArray, 1));

[Salad Box]

Many thanks! Your solutions are also perfect for this task!