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How to extract data from strcture ?

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Abdelwahab Fawzy
Abdelwahab Fawzy 2016-7-16
编辑： per isakson 2016-7-17
if i have a structure of 101 nodes, i want to extract the data of the first 99 nodes only in an array

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采纳的回答

Image Analyst
Image Analyst 2016-7-16
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.

更多回答（1 个）

per isakson
per isakson 2016-7-16
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
  2 个评论
Walter Roberson
Walter Roberson 2016-7-17
Or you could struct2cell(), extract the appropriate components of the cell, and cell2struct() the result.
per isakson
per isakson 2016-7-17
编辑：per isakson 2016-7-17
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

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