How to extract data from strcture ?

if i have a structure of 101 nodes, i want to extract the data of the first 99 nodes only in an array

[per isakson]

Depends on what you mean by "node"

Answer 1

[Image Analyst]

If you have a structure array of more than 100 "elements", then you can extract the first 99 like this:

s99 = s(1:99);

This will extract the first 99 into another variable, s99, and all "fields" of the structure will also be brought along.

Answer 2

[per isakson]

If you by "node" mean what is called field in Matlab

    %%create a stucture with 101 fields
    sas = cell2struct( num2cell(1:101)                            ...
        , arrayfun( @(x)sprintf('F%03d',x),(1:101), 'uni',false ) ...
        , 2 );
    %%extract the data of the first 99 fields
    len = 99;
    M   = nan(1,len);
    field_list = fieldnames( sas );
    for jj = 1 : len
        M(jj) = sas.(field_list{jj});
    end

[Walter Roberson]

Or you could struct2cell(), extract the appropriate components of the cell, and cell2struct() the result.

[per isakson]

Yes, struct2cell provides a more compact code. Try

>> cssm
Elapsed time is 0.000301 seconds.
Elapsed time is 0.000241 seconds.
ans =
     1
Elapsed time is 0.000101 seconds.
ans =
     1

where

function  cssm( )
%%create a stucture with 101 fields
sas = cell2struct( num2cell(1:101)                            ...
    , arrayfun( @(x)sprintf('F%03d',x),(1:101), 'uni',false ) ...
    , 2 );
len = 99;
%%use for-loop to extract the data of the first 99 fields
tic
M1  = nan(len,1);
field_list = fieldnames( sas );
for jj = 1 : len
    M1(jj) = sas.(field_list{jj});
end
toc
%%use struct2cell and cell2mat to extract the data of the first 99 fields
tic
cac = struct2cell( sas );
M2  = cell2mat( cac(1:len) );
toc
all( M2 == M1 )
%%use struct2cell and cat to extract the data of the first 99 fields
tic
cac = struct2cell( sas );
M3  = cat( 1, cac{1:len} );
toc
all( M3 == M1 )
end