6.2.4 Cell Arrays of Strings

One common use of cell arrays is to store multiple strings in the same variable. It is also possible to store multiple strings in a character matrix by letting each row be a string. This, however, introduces the problem that all strings must be of equal length. Therefore, it is recommended to use cell arrays to store multiple strings. For cases, where the character matrix representation is required for an operation, there are several functions that convert a cell array of strings to a character array and back. char and strvcat convert cell arrays to a character array (see section Concatenating Strings), while the function cellstr converts a character array to a cell array of strings:

a = ["hello"; "world"];
c = cellstr (a)
     ⇒ c =
         {
           [1,1] = hello
           [2,1] = world
         }

Built-in Function: cellstr (string)

Create a new cell array object from the elements of the string array string.

One further advantage of using cell arrays to store multiple strings is that most functions for string manipulations included with Octave support this representation. As an example, it is possible to compare one string with many others using the strcmp function. If one of the arguments to this function is a string and the other is a cell array of strings, each element of the cell array will be compared to the string argument:

c = {"hello", "world"};
strcmp ("hello", c)
     ⇒ ans =
        1   0

The following string functions support cell arrays of strings: char, strvcat, strcat (see section Concatenating Strings), strcmp, strncmp, strcmpi, strncmpi (see section Comparing Strings), str2double, deblank, strtrim, strtrunc, strfind, strmatch, , regexp, regexpi (see section Manipulating Strings) and str2double (see section String Conversions).

The function iscellstr can be used to test if an object is a cell array of strings.

Built-in Function: iscellstr (cell)

Return true if every element of the cell array cell is a character string

Function File: [idxvec, errmsg] = cellidx (listvar, strlist)

Return indices of string entries in listvar that match strings in strlist.

Both listvar and strlist may be passed as strings or string matrices. If they are passed as string matrices, each entry is processed by deblank prior to searching for the entries.

The first output is the vector of indices in listvar.

If strlist contains a string not in listvar, then an error message is returned in errmsg. If only one output argument is requested, then cellidx prints errmsg to the screen and exits with an error.