Making structure arrays programmtically.

Hello Guys,

I have been trying to do the following programmatically and I have not been successful so far (excuse my ignorance if this is a trivial problem for most of you).

I have the following data:

Day of Month Temperature Pressure Day1 15 101.3 Day2 25 98

I want a structure, for example, mystruct to look like below.

mystruct.Dayofmonth = {'Day1'; 'Day2'} mystruct.Temperature = [15 ; 25]; mystruct.Pressure = [101.3; 98];

My aim is to group all the temperatures under 'temperature' field and pressures under 'pressure' (and similarly the day of the month field also). I would like to do this programatically so that I can use this concept for creating such structures dynamically(i.e., without having to hard code the name of the fields).

This is my first post under mathworks answers. I have been a great fan of the products and of the openmindedness to share ideas in this group.

Thanks. -Mahesh

[Mahesh]

Sorry... the table did not come through correctly. its the table of Dayofmonth, Temperature and Pressure as columns.

[Oleg Komarov]

How do you retrieve the source data. Is it always on one line?

[Mahesh]

The data is in columns each column is a variable (time)that has data for a period of time. Did I answer your question?

[Oleg Komarov]

DO you have it on .txt with headers?

[Mahesh]

No. I have it in .xls with headers.

Answer 1

[Oleg Komarov]

If you have the stats TB you can import a file directly as a dataset object.

It is very convenient and easy to use.

EDIT

I have created the following xlsx file:

A  B  C
1  5  9
2  6  10
3  7  11
4  8  12

Now to create programmatically the structure (independently on the number of columns):

[data,text] = xlsread('test.xlsx');
In = [text;num2cell(data,1)];
S  = struct(In{:});

Or if you want a non-scalar structure create first In as:

In = [text;num2cell(num2cell(data),1)];

[Mahesh]

Thanks this is perfect.

Also, What if Column A is made of strings not numbers? Also, how does the second line of your code work? Are you trying to concatenate strings with cells?

Thanks for all the help. I have been trying to understand this concept for a long time.

[Oleg Komarov]

1) Col A strings: you have to pack the column A that you will find in the text variable into a cell and concatenate it to num2cell(data,1)

2) second line: take text (which in my case contains only the a row array of headers {'a','b','c'} and below it attach the columns packed into cells [{'a','b','c'}; {(1:4).';(5:8).';(9:12).'}]

Answer 2

[Robert Cumming]

you can make fields in a structure dynamically, i.e.

    yourStruct.(yourVariable) = value

The fields in your structure can be accessed incrementally i.e.

    yourStruct.(yourVariable)(index)

etc....

Answer 3

[Fangjun Jiang]

Yes, the structure array would be perfect for your need. Based on your sample data, you can do.

Dayofmonth = {'Day1'; 'Day2'};
Temperature = [15 ; 25];
Pressure = [101.3; 98];

Temperature=mat2cell(Temperature,ones(size(Temperature)),1);
Pressure=mat2cell(Pressure,ones(size(Pressure)),1);

mystruct=struct('Dayofmonth',Dayofmonth,'Temperature',Temperature,'Pressure',Pressure)
mystruct(1)
mystruct(2)
[mystruct.Temperature]
mystruct = 

2x1 struct array with fields:
    Dayofmonth
    Temperature
    Pressure

ans = 

       Dayofmonth: 'Day1'
      Temperature: 15
         Pressure: 101.3000

ans = 

       Dayofmonth: 'Day2'
      Temperature: 25
         Pressure: 98

[Mahesh]

Yes. This is what I had in mind. But I have several fields and I dont want to use the command struct to manually input the fieldnames. Is there a way to construct the structure dynamically (without hardcoding the field names)?

[Fangjun Jiang]

To have meaningful field names like Temperature and Pressure, you have to specify it manually one way or another. You could generate field names programmatically, such as,

a=struct('FirstField',1);

for k=2:3

FieldName=['Field',num2str(k)];

a=setfield(a,FieldName,k);

end

BTW, I modified my original code to use function ones(), instead of repmat().

[Fangjun Jiang]

If you mean dynamic field name, you could also do.

a=struct('FirstField',1);

for k=2:3

FieldName=['Field',num2str(k)];

a.(FieldName)=k;

end