keepfield(instruct,fields)

function outstruct = keepfield(instruct,fields)
% OUTSTRUCT = KEEPFIELD(INSTRUCT,FIELDNAMES)
% Removes all fields from a structure other than those specified in 
% input variable FIELDS. 
%
% FIELDS may be a single field, or a cell array of field names
%
% ex:
% a = dir('*.m');
% b = keepfield(a,{'name','bytes'});
%
% See also: rmfield
%
% Written by Brett Shoelson, PhD
% 3/1/05
% [e-mail]

if nargin ~= 2
	error('Requires 2 input arguments.');
end
if ~isa(instruct,'struct')
	error('The first input argument must be a structure.');
end
if (~isa(fields,'char') & ~isa(fields,'cell')) | (isa(fields,'cell') & ~all(cellfun('isclass',fields,'char')))
	error('The second input argument must be a string representing the name of a field to keep or a cell array of field names to keep.');
end

outstruct = rmfield(instruct,setdiff(fieldnames(instruct),fields));