Setting up my structure with a cell array of char vectors.

I need a structure to contain a cell array of character vectors (cell array of strings). The structure looks OK if I just set up a character array, but when I change it to an cell array of strings, my structure dimensions change. The culprit is field 'b'. In the example below, struct1 has the correct dimensions (1x1), but 'b' is just a char array. When I change 'b' to a cell array of strings, as in struct2, the structure dimensions change (3x3).

struct1 = struct('a',char(zeros(10,1)),'b',['3';'4';'7'],...
   'c',zeros(10,1),'d',zeros(10,3),'e',zeros(10,3),...
   'f',zeros(10,1),'g',zeros(10,1),'h',zeros(10,1));    

struct2 = struct('a',char(zeros(10,1)),'b',cellstr(['3';'4';'7']),...
  'c',zeros(10,1),'d',zeros(10,3),'e',zeros(10,3),...
  'f',zeros(10,1),'g',zeros(10,1),'h',zeros(10,1));

What am I missing? Please help!

Answer 1

[James Tursa]

You are missing a special "feature" of the struct function when one of the inputs is a cell array:

https://www.mathworks.com/help/matlab/ref/struct.html?searchHighlight=struct

From this link:

If value is not a cell array, then s is a scalar structure, where s.(field) = value.

If value is a cell array, then s is a structure array with the same dimensions as value. Each element of s contains the corresponding element of value. For example, s = struct('f',{'a','b'}) returns s(1).f = 'a' and s(2).f = 'b'.

This can be irritating at times when you don't want that 2nd behavior. So you will be forced to re-code things to build the struct a bit piecemeal if you want that cell array to be part of the struct in the same manner as the char array.

[Walter Roberson]

Yup, this has bitten me more than once.

[Bryan Wilson]

THANKS! What worked for me was...

struct1 = struct('a',char(zeros(10,1)),...
   'c',zeros(10,1),'d',zeros(10,3),'e',zeros(10,3),...
   'f',zeros(10,1),'g',zeros(10,1),'h',zeros(10,1)); 

bData = cellstr(['3';'4';'7']);

[struct1(:).b] = bData;

FYI, this puts field b at the bottom of the structure. You can reorder with some creativity.

[per isakson]

"when you don't want that 2nd behavior" &nbsp add an extra pair of braces

sa1 = struct( 'f1', {num2cell(1:6)} );
sa2 = struct( 'f1', num2cell(1:6) );
whos sa*

outputs

    Name      Size            Bytes  Class     Attributes
    sa1       1x1               896  struct              
    sa2       1x6               784  struct

or I didn't read carefully enough