Help with rowfun?

I've created a table with columns Go,Export, and Directory and row names from a list of strings (ex {'First Row','Second Row'})

I have a helper function, generic_helper that takes each of a Go, Export, and Directory values from a table, along with the string corresponding to the row (ex 'First Row') and a binary flag that does not change across rows.

How can I apply rowfun to call generic_helper(Go,Export,Directory,rowName,ex_bin_flag) for the values of Go,Export,Directory, and rowName in each row of my table?

Thanks in advance!

[Rik]

Have you considered a for-loop? If so, why doesn't that do what you need?

[amen45]

I have one now, but as I understand with tables in matlab vectorizing is particularly advantageous in terms of speed (unlike say cellfun for cell arrays). if I'm mistaken, I'd love an explanation!

Answer 1

[Rik]

You should have the helper function with some output (one or multiple scalars (single values)). Then, in your code you can use

newtable=rowfun(@generic_helper,table);

Note from rowfunc doc: "To return more than one output from func, use the 'NumOutputs' or 'OutputVariableNames' name-value pair arguments."

PS you were correct in looking for a vectorized solution, they are indeed generally faster. For smaller problems the effect is often negligible, but it always affects readability.

[amen45]

Thank you! Do you have guidance on how to incorporate the outside binary flag and the row name? That was the part that confused me in the documentation

[Rik]

How do you need to incorporate them? If you need multiple outputs in newtable, just try something like

newtable=rowfun(@generix_helper,table,'OutputVariableNames',{'CalculatedValue','bin_flag','RowName'});

[amen45]

Sorry, I think I asked the question poorly. Behavior within generic_helper is dictated by the RowName and the binary flag. The binary flag turns off user warnings, so it's constant across all rows, as is a src directory string I forgot to include above. Does that make sense?

For example, my for loop right now looks something like this:

rnames = table.Properties.RowNames;

for curr_row = 1:length(rnames)

    new_table{rnames{curr_row},'Directory'} = generic_helper (table{rnames{curr_row},'Go'},...
        table{rnames{curr_row},'Export'},table{rnames{curr_row},'Directory'}, ...
        src_dir_string,rnames{curr_row}, warning_flag_off);
end

Thanks for your help with this!

[Rik]

I was not aware that you could use a string as row-index and still get your intended behavior. As long as you make sure that the table you feed to rowfun has as many columns as generic_helper has inputs, the line in the main answer body should work.

[amen45]

yes, but the reason I need help is that I have 2 pieces of information that are not in the table, and I don't want to include them in the table, since they apply to all the rows in the same way. Is this not possible?

[Rik]

It is possible with a global variable. Those should generally be avoided, but I don't see another solution right now. What is the harm in creating a temporary table that does include those pieces of information?

[amen45]

Right now these are global variables, because I need them elsewhere. Does that help? I can try creating a temporary table if necessary, or just keep the for loop, if this isn't possible.

[Rik]

Global variables are best avoided, because they make code difficult to debug and can be unpredictable if edited somewhere unexpected. You can just call global bin_flag rowName inside the helper function and it should work.

[amen45]

sorry, should have been more specific. they are globals that are passed to the generic helper function, as shown in my example code above. This is all happening in a larger module.

[Rik]

Well, then you can either declare bin_flag and rowName as global variables, or create two new global variables in which you paste the content of bin_flag and rowName.