Removing a field from a Linked List (MatLab) - matlab

Question

I have a one way linked list:
s=struct('field1', value1, 'field2', value2, 'field3', value3, 'next',[])
s=struct('field1', value3, 'field2', value5, 'field3', value6, 'next', s)
How do I remove the 'next' field so that my linked list becomes a standard structure array, like so?
s(1)=struct('field1', value1, 'field2', value2, 'field3', value3)
s(2)=struct('field1', value3, 'field2', value5, 'field3', value6)
I have tried the rmfield command but I get a 1x1 structure array, but I want, in this example, a 1x2 structure array.

Answer 1

You will want to first aggregate all of your structs together. You could use a recursive function to do this. Then you can call rmfield on the array of structs. You could also even combine the two at the same time.
function S = flattenList(S)
if isempty(S.next)
S = rmfield(S, 'next');
else
S = cat(2, rmfield(S, 'next'), flattenList(S.next));
end
end
As pointed out in the comments, since we are constantly appending data to the output, it can be slow for larger lists. We could determine the expected output size and then fill it within the loop.
This approach would allow you to pre-allocate the output.
function output = flattenList(S)
% Determine how big to make the output
tmp = S;
count = 1;
while ~isempty(tmp.next)
count = count + 1;
tmp = tmp.next;
end
% Pre-allocate the output
output = repmat(rmfield(S(1), 'next'), [1 count]);
tmp = S;
count = 1;
while true
output(count) = rmfield(tmp, 'next');
if isempty(tmp.next)
break;
else
tmp = S.next;
end
end
end