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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.

Function File: columns (a)

Return the number of columns of a.

Function File: rows (a)

Return the number of rows of a.

Function File: length (a)

Return the number of rows of a or the number of columns of a, whichever is larger.

Function File: 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 2 element row vector. If there are two output arguments, the number of rows is assigned to the first, and the number of columns to the second. 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 of either 1 or 2, size will return only the row or column dimension. For example

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

returns the number of columns in the given matrix.

Function File: 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.