How to convert cell array to structure array

I would like to convert cell array to a structure 1x2 (or 2x1) with 3 fields with a1 as dimension/axis:

a1={'AA','AA','AA','BB','BB','BB','BB'}';
a2={'35000','96000','88000','33000','44000','8000','18000'}';
a3={'1a','1b','1c','1d','1e','1a','1b'}';
a123=[a1,a2,a3];
rowHeadings = {'first', 'second', 'third'};

but this does not work:

depts = cell2struct(a123, rowHeadings, 1)

Error using cell2struct
Unknown command option.

[Geoff Hayes]

Aleksander - which version of MATLAB are you using? If I try the above, on R2014a, and change the depts initialization to

 depts = cell2struct(a123', rowHeadings, 1)

then it works fine, with

 depts = 
 7x1 struct array with fields:
    first
    second
    third

Note that the transpose of a123 is necessary since rowheadings is a 1x3 cell array, and so the first input to cell2struct must be a 3x7.

[Aleksandar]

Geoff thank you - it works. However now I have 7x1 struct with 3 fields. But I should have 1x2 structure (one for AA and second for BB)as they are distinct categories with 3 fields (which is ok). That is to say I want to group AAs and BBs in 2 categories.

[Aleksandar]

...a2 and a3 should be vectors instead.

[Geoff Hayes]

Aleksander - please provide an example of how you would like the structure to appear. Also, what do you mean by a2 and a3 should be vectors instead? Aren't they already arrays?

[Aleksandar]

I would like structure to appear like that: First Second Third AA [35000 96000 88000] [1a 1b 1c] BB [33000 44000 8000 18000] [1d 1e 1a 1b] The grouping categories is data in rowheadings first, i.e.: 'AA' and 'BB' (as if in idTotals in Credit risk utitilites)

[Stephen23]

@Aleksandar: it looks like you are a bit confused about what structures can do. Structures are not really categorization tools, nor are they dictionaries (which might look similar to what you wrote above). Like most traditional MATLAB data classes the dimensions of a structure do not encode any meta-data, so you cannot "name" the dimensions of a 1x2 structure 'AA' and 'BB', atleast not as meta-data in the structure itself. It would be possible to either:

• create a separate array containing this data, or
• include this meta-data as data withing the structure (see my answer below).
• use another data class: it seems like you might really be looking for something more like a table. Have you looked at using one?

[Vahab Youssofzadeh]

Try the following:

table2struct(cell2table(.))

Answer 1

[Azzi Abdelmalek]

a1={'AA','AA','AA','BB','BB','BB','BB'}';
a2={'35000','96000','88000','33000','44000','8000','18000'}';
a3={'1a','1b','1c','1d','1e','1a','1b'}';
a123=[a1,a2,a3];
rowHeadings = {'first', 'second', 'third'};
v=cell2struct(a123,rowHeadings,2)

[Aleksandar]

Hi Azzi, is there a possibility to convert it to 1x2 structure with 3 fields (AA i BB groups)?

[Azzi Abdelmalek]

a1={'AA','AA','AA','BB','BB','BB','BB'}';
a2={'35000','96000','88000','33000','44000','8000','18000'}';
a3={'1a','1b','1c','1d','1e','1a','1b'}';
a123=[a1,a2,a3];
rowHeadings = {'first', 'second', 'third'};
ii=unique(a1)
for k=1:numel(ii)
  idx=ismember(a1,ii{k})
  v(k).first=ii{k}
  v(k).second=a2(idx)
  v(k).third=a3(idx)
end

[Stephen23]

Note that it is poor practice in MATLAB to expand arrays inside loops, even for structures and cell arrays:

http://blogs.mathworks.com/loren/2008/02/01/structure-initialization/

http://www.mathworks.com/help/matlab/matlab_prog/memory-allocation.html

It is better either to create the entire structure in one call (see my answer), or to preallocate the structure (e.g. looping in reverse).

Answer 2

[Stephen23]

Here is a short and reasonably tidy way of doing this using struct:

a1 = {'AA','AA','AA','BB','BB','BB','BB'}';
a2 = {'35000','96000','88000','33000','44000','8000','18000'}';
a3 = {'1a','1b','1c','1d','1e','1a','1b'}';
hdr = {'first', 'second', 'third'};
fun = @(x)arrayfun(@(s)x(strcmp(s,a1)), unique(a1,'stable'), 'UniformOutput',false);
X = struct(hdr{1},fun(a1), hdr{2},fun(a2), hdr{3},fun(a3));

Now lets check it in the command window:

>> X
X = 
2x1 struct array with fields:
    first
    second
    third
>> X.first
ans = 
    'AA'
    'AA'
    'AA'
ans = 
    'BB'
    'BB'
    'BB'
    'BB'
>> X.second
ans = 
    '35000'
    '96000'
    '88000'
ans = 
    '33000'
    '44000'
    '8000'
    '18000'

[Aleksandar]

Thank you! I accepted the answer(s) , I suppose it refers to both answers.

[Stephen23]

"I suppose it refers to both answers"

No, it doesn't. You can vote for other answers though.