sortStruct2(aStruct, fieldName, direction, check)

function [sortedStruct index] = sortStruct2(aStruct, fieldName, direction, check)
% [sortedStruct index] = sortStruct2(aStruct, fieldName, direction)
% sortStruct2 returns a sorted struct array, and can also return an index vector. The
% (one-dimensional) struct array is sorted based on the field specified by the string
% fieldName. The field must a single number or logical, or a char array (usually a simple
% string).
%
% direction is an optional argument to specify whether the struct array should be sorted
% in ascending or descending order. By default, the array will be sorted in ascending
% order. If supplied, direction must equal 1 to sort in ascending order or -1 to sort in
% descending order.
%
% check is an optional argument that should not be used if calling sortStruct2 directly.
% Calls to sortStruct2 by nestedSortStruct2 use check to bypass checking inputs. If check
% equals 1 or is not given, inputs are checked. If check equals 0, inputs are not checked.

%% check inputs
if nargin < 4 || check
    if ~isstruct(aStruct)
        error('first input supplied is not a struct.')
    end % if
    
    if sum(size(aStruct)>1)>1 % if more than one non-singleton dimension
        error('I don''t want to sort your multidimensional struct array.')
    end % if
    
    if ~ischar(fieldName) || ~isfield(aStruct, fieldName)
        error('second input is not a valid fieldname.')
    end % if
    
    if nargin < 3
        direction = 1;
    elseif ~isnumeric(direction) || numel(direction)>1 || ~ismember(direction, [-1 1])
        error('direction must equal 1 for ascending order or -1 for descending order.')
    end % if
end % if check

%% figure out the field's class, and find the sorted index vector
fieldEntry = aStruct(1).(fieldName);

if (isnumeric(fieldEntry) || islogical(fieldEntry)) && numel(fieldEntry) == 1 % if the field is a single number
    [dummy index] = sort([aStruct.(fieldName)]);
elseif ischar(fieldEntry) % if the field is char
    [dummy index] = sort({aStruct.(fieldName)});
else
    error('%s is not an appropriate field by which to sort.', fieldName)
end % if ~isempty

%% apply the index to the struct array
if direction == 1 % ascending sort
    sortedStruct = aStruct(index);
else % descending sort
    sortedStruct = aStruct(index(end:-1:1));
end