octave: Object Sizes
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.
-- : ndims (A)
Return the number of dimensions of A.
For any array, the result will always be greater than or equal to
2. Trailing singleton dimensions are not counted.
ndims (ones (4, 1, 2, 1))
⇒ 3
See also: 
size XREFsize.
-- : columns (A)
Return the number of columns of A.
DONTPRINTYET See also: rows XREFrows, size XREFsize, *notelength:
DONTPRINTYET See also: rows XREFrows, size XREFsize, length
XREFlength, numel XREFnumel, isscalar XREFisscalar,
isvector XREFisvector, ismatrix XREFismatrix.
-- : rows (A)
Return the number of rows of A.
DONTPRINTYET See also: columns XREFcolumns, size XREFsize, *noteDONTPRINTYET DONTPRINTYET See also: columns XREFcolumns, size XREFsize,
length XREFlength, numel XREFnumel, *noteisscalar:
DONTPRINTYET DONTPRINTYET DONTPRINTYET See also: columns XREFcolumns, size XREFsize,
length XREFlength, numel XREFnumel, isscalar
XREFisscalar, isvector XREFisvector, *noteismatrix:
DONTPRINTYET DONTPRINTYET DONTPRINTYET See also: columns XREFcolumns, size XREFsize,
length XREFlength, numel XREFnumel, isscalar
XREFisscalar, isvector XREFisvector, ismatrix
XREFismatrix.
-- : numel (A)
-- : numel (A, IDX1, IDX2, ...)
Return the number of elements in the object A.
Optionally, if indices IDX1, IDX2, ... are supplied, return the
number of elements that would result from the indexing
A(IDX1, IDX2, ...)
Note that the indices do not have to be scalar numbers. For
example,
A = 1;
B = ones (2, 3);
numel (A, B)
will return 6, as this is the number of ways to index with B. Or
the index could be the string ":" which represents the colon
operator. For example,
A = ones (5, 3);
numel (A, 2, ":")
will return 3 as the second row has three column entries.
This method is also called when an object appears as lvalue with
cs-list indexing, i.e., ‘object{...}’ or ‘object(...).field’.
DONTPRINTYET See also: size XREFsize, length XREFlength, *noteDONTPRINTYET See also: size XREFsize, length XREFlength,
ndims XREFndims.
-- : length (A)
Return the length of the object A.
The length is 0 for empty objects, 1 for scalars, and the number of
elements for vectors. For matrix or N-dimensional objects, the
length is the number of elements along the largest dimension
(equivalent to ‘max (size (A))’).
See also: numel XREFnumel, size XREFsize.
-- : SZ = size (A)
-- : DIM_SZ = size (A, DIM)
-- : [ROWS, COLS, ..., DIM_N_SZ] = size (...)
Return a row vector with the size (number of elements) of each
dimension for the object A.
When given a second argument, DIM, return the size of the
corresponding dimension.
With a single output argument, ‘size’ returns a row vector. When
called with multiple output arguments, ‘size’ returns the size of
dimension N in the Nth argument. The number of rows, dimension 1,
is returned in the first argument, the number of columns, dimension
2, is returned in the second argument, etc. If there are more
dimensions in A then there are output arguments, ‘size’ returns the
total number of elements in the remaining dimensions in the final
output argument.
Example 1: single row vector output
size ([1, 2; 3, 4; 5, 6])
⇒ [ 3, 2 ]
Example 2: number of elements in 2nd dimension (columns)
size ([1, 2; 3, 4; 5, 6], 2)
⇒ 2
Example 3: number of output arguments == number of dimensions
[nr, nc] = size ([1, 2; 3, 4; 5, 6])
⇒ nr = 3
⇒ nc = 2
Example 4: number of output arguments != number of dimensions
[nr, remainder] = size (ones (2, 3, 4, 5))
⇒ nr = 2
⇒ remainder = 60
DONTPRINTYET See also: numel XREFnumel, ndims XREFndims, *noteDONTPRINTYET DONTPRINTYET See also: numel XREFnumel, ndims XREFndims,
length XREFlength, rows XREFrows, *notecolumns:
DONTPRINTYET DONTPRINTYET DONTPRINTYET See also: numel XREFnumel, ndims XREFndims,
length XREFlength, rows XREFrows, columns
XREFcolumns, size_equal XREFsize_equal, *notecommon_size:
DONTPRINTYET DONTPRINTYET DONTPRINTYET See also: numel XREFnumel, ndims XREFndims,
length XREFlength, rows XREFrows, columns
XREFcolumns, size_equal XREFsize_equal, common_size
XREFcommon_size.
-- : isempty (A)
Return true if A is an empty matrix (any one of its dimensions is
zero).
See also: isnull XREFisnull, isa XREFisa.
-- : isnull (X)
Return true if X is a special null matrix, string, or single quoted
string.
Indexed assignment with such a value on the 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.
See also: isempty XREFisempty, isindex XREFisindex.
-- : sizeof (VAL)
Return the size of VAL in bytes.
See also: whos XREFwhos.
-- : size_equal (A, B, ...)
Return true if the dimensions of all arguments agree.
Trailing singleton dimensions are ignored. When called with a
single argument, or no argument, ‘size_equal’ returns true.
DONTPRINTYET See also: size XREFsize, numel XREFnumel, *noteDONTPRINTYET See also: size XREFsize, numel XREFnumel,
ndims XREFndims, common_size XREFcommon_size.
-- : 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.
See also: reshape XREFreshape.
Info Catalog
octave: User-defined Data Types
octave: Data Types