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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.

— 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.

— 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.