Deleting or selecting rows of a struct with a condition

Dear All, I would like to delete or select the rows of a struct by checking the value of a column. For example in the bellow, I say if the value was not 'p' and not 'h', then delete the row.

for i=1:numel(logfile)
if (logfile(i).code ~= 'p') && (logfile(i).code ~= 'H')
logfile(i)=[];
end
end

It only deletes one row, The error that i get is as follow:

Operands to the || and && operators must be convertible to logical scalar values.

Would you please give me some tips?

If i wanted to filter the rows with code value of 'p', then what should I do?

I tried this

logfile([logfile.code == 'p'])

but the error code is as follows :

Index exceeds matrix dimensions.

Thank you in advance.

Answer 1

[James Tursa]

The first part, assuming the .code fields are all 1 character:

logfile_code = [logfile.code]; % Get all the codes
g = logfile_code == 'p' | logfile_code == 'H'; % Find the p and H codes
logfile = logfile(g); % Select only the p and H codes, delete the rest

The second part:

g = logfile_code == 'p'; % Find the p codes
logfile_p = logfile(g); % Select only the p code rows

If the .code fields could be any length string and not single characters, then you could use a cell array of strings instead. E.g.,

logfile_code = {logfile.code};
g = strcmp(logfile_code,'p') | strcmp(logfile_code,'H');
logfile = logfile(g); % Select only the p and H codes, delete the rest

and

g = strcmp(logfile_code,'p');
logfile_p = logfile(g); % Select only the p code rows

Answer 2

[Azzi Abdelmalek]

Don't use ==

for i=1:numel(logfile)
   if ~isequal(logfile(i).code,'p') && ~isequal(logfile(i).code,'H')
      logfile(i)=[];
   end
end

Answer 3

[Guillaume]

Most likely, you're getting the error with && because some of your code strings are more than one character. See the output of:

'xyz' ~= 'p'

As a rule, if you're going to compare strings always use strcmp (or its companions strcmpi, strncmp, strncmpi) which will always return a scalar regardless of the length of the string. So,

if ~strcmp(logfile(i).code,'p') && ~strcmp(logfile(i).code, 'H')

will fix your problem.

But you're using a loop, and that's not efficient. You were on the right track with your other expression. Again, you should be using strcmp and you should concatenate all the codes into a cell array rather than a vector, so:

logfile(~strcmp({logfile.code}, 'p') & ~strcmp({logfile.code}, 'H')) = [] %no need for loop

Finally, rather than doing two strcmp, you can use ismember (which uses strcmp internally), so it becomes:

logfile(~ismember({logfile.code}, {'p', 'H'}) = [];