MATLAB creating of struct-vector

Question

Given some data - for example (in my case) - like the following tabular

Name  |pos_x|pos_y|pos_z
------------------------
Point1|   .1|   .1|   .2
Point2|  0.0|  0.0|   .1
Middle|   .1|   .2|   .1
Point3|  0.0|    1|  0.0

and maybe after importing that data from excel all values are stored in a cell array (lets call it celldata).
For testing purposes this cell could be created with the line

celldata={'Point1' .1 .1 .2;'Point2' 0 0 .1;'Middle' .1 .2 .1;'Point3' 0 1 0}

For this example the cell is of size 4x4.

At the moment I'm creating a structure with the following lines

point.name=char(celldata(:,1));
point.posxyz=cell2mat(celldata(:,2:4));

This results in point size 1x1 Class struct. I'm looking for an efficient way to generate it as point size 4x1 Class struct - thus one element for each line in the tabular above - all with the same inner structure: a name and the coordinates.
I already tried cell2struct, but that is only able to unfold along one dimension without grouping some colums together - as far as I tried.
Further, this is not a duplicate of Preallocate structure of cells in matlab as in this case here, I have many different columns - or maybe even a dynamic count of columns.

I think it would be fine for looping over the elements: for punkt=point,disp([punkt.name ':' num2str(norm(punkt.posxyz))]),end as an example. Especially one does not need to check how many elements there are. Do you know anything better? — Bastian Ebeling
– Bastian Ebeling, Commented Apr 29, 2013 at 8:50

Dan · Accepted Answer · 2013-04-29 10:54:43Z

1

cellData = {'Name', 'pos_x', 'pos_y'; 'Harry', 34, 2; 'Bernard', 5, 11}

Then

for col = 1:size(cellData ,2)
    fieldName = cellData{1, col};
    c = cellData (2:end, col);
    [point(1:length(c)).(fieldName)] = c{:};
end

Now

point(1)

ans = 

     Name: 'Harry'
    pos_x: 34
    pos_y: 2

point(2)

ans = 

     Name: 'Bernard'
    pos_x: 5
    pos_y: 11

EDIT:

If you want to only have 2 fields, i.e. Name and posxyz then:

 [M, N] = size(celldata);
 names = celldata(:,1);
 [point(1:M).Name] = names{:};
 xyz = mat2cell(cell2mat(celldata(:,2:end)), ones(M,1), N - 1);
 [point(1:M).posxyz] = xyz{:};

now for celldata={'Point1' .1 .1 .2;'Point2' 0 0 .1;'Middle' .1 .2 .1;'Point3' 0 1 0}

point(1)

ans = 

          Name: 'Point1'
        posxyz: [0.1000 0.1000 0.2000]

point(2)

ans = 

      Name: 'Point2'
    posxyz: [0 0 0.1000]

edited Apr 29, 2013 at 10:54

answered Apr 29, 2013 at 8:50

Dan

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7 Comments

Bastian Ebeling Over a year ago

Thanks @Dan for this idea, but I really don't like the need to assign the names (for example) one by another. Please think about a table with some hundreds or more lines. Further ideas?

Bastian Ebeling Over a year ago

Adding could of course be done like done within rmfield.m - but I think this should be possible some faster, or?

Dan Over a year ago

@BastianEbeling hundreds of lines or hundreds of columns?

Bastian Ebeling Over a year ago

Hi Dan, in my comment I ment hundreds of lines. But (as in my last edit, which you might not have seen) there could also occur many columns.

Dan Over a year ago

@BastianEbeling Well lines obviously isn't a problem, just replace the 4 with length(C), for the columns, I think your best bet is a simple for loop, so if col is the loop variable and C = celldata{:, col} then [point(1:length(C), col).(C{1})] = C{2:end}

|

Eitan T · Accepted Answer · 2013-04-29 10:23:55Z

1

Try using struct with cell arrays as input:

C = cellfun(@(x,y,z)[x y z], celldata(:,2), celldata(:,3), celldata(:,4), 'Uniform', 0);
point = struct('name', celldata(:, 1), 'posxyz', C);

Notice that for the posxyz field I've created a new cell array by catenating the cells of celldata.

If you want to add another field later, you can use deal and comma-separated lists. The following example stores the values from the fourth column of celldata in a new field, called pos_z:

[point(:).pos_z] = deal(celldata{:, 4});

edited Apr 29, 2013 at 10:23

answered Apr 29, 2013 at 8:57

Eitan T

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2 Comments

Bastian Ebeling Over a year ago

Thank you, this is a really fine idea. In my case there are many more columns - and for readability I wanted to add each column (or pair of columns like in xyz) in one source-code line. Do you know a way to add fields to your created point-structure?

Eitan T Over a year ago

@BastianEbeling Of course. You'll need to use deal and comma-separated lists. See the revised answer.

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