info octave

3.3 Object Sizes

The following functions allow you to determine the size of a variable or expression. These functions are defined for all objects. They return -1 when the operation doesn't make sense. For example, Octave's data structure type doesn't have rows or columns, so the rows and columns functions return -1 for structure arguments.

Built-in Function: ndims (a): Returns the number of dimensions of array a. For any array, the result will always be larger than or equal to 2. Trailing singleton dimensions are not counted.

Built-in Function: columns (a)

Return the number of columns of a.

See also: size, numel, rows, length, isscalar, isvector, ismatrix.

Built-in Function: rows (a)

Return the number of rows of a.

See also: size, numel, columns, length, isscalar, isvector, ismatrix.

Built-in Function: numel (a)

Returns the number of elements in the object a.

See also: size.

Built-in Function: length (a): Return the `length' of the object a. For matrix objects, the length is the number of rows or columns, whichever is greater (this odd definition is used for compatibility with MATLAB).

Built-in Function: size (a, n)

Return the number rows and columns of a.

With one input argument and one output argument, the result is returned in a row vector. If there are multiple output arguments, the number of rows is assigned to the first, and the number of columns to the second, etc. For example,

size ([1, 2; 3, 4; 5, 6])
     ⇒ [ 3, 2 ]

[nr, nc] = size ([1, 2; 3, 4; 5, 6])
     ⇒ nr = 3
     ⇒ nc = 2

If given a second argument, size will return the size of the corresponding dimension. For example

size ([1, 2; 3, 4; 5, 6], 2)
     ⇒ 2

returns the number of columns in the given matrix.

See also: numel.

Built-in Function: isempty (a): Return 1 if a is an empty matrix (either the number of rows, or the number of columns, or both are zero). Otherwise, return 0.

Built-in Function: isnull (x)

Return 1 if x is a special null matrix, string or single quoted string. Indexed assignment with such a value as right-hand side should delete array elements. This function should be used when overloading indexed assignment for user-defined classes instead of isempty, to distinguish the cases:

A(I) = []: This should delete elements if I is nonempty.
X = []; A(I) = X: This should give an error if I is nonempty.

Built-in Function: sizeof (val): Return the size of val in bytes

Built-in Function: size_equal (a, b, …)

Return true if the dimensions of all arguments agree. Trailing singleton dimensions are ignored. Called with a single argument, size_equal returns true.

See also: size, numel.

Built-in Function: squeeze (x): Remove singleton dimensions from x and return the result. Note that for compatibility with MATLAB, all objects have a minimum of two dimensions and row vectors are left unchanged.

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