Re-assigning numerical subjects IDs to string user IDs from experimental data

I'm at a very basic level so need basic answers!

The experimental data I have received has each subejct given a random string as their user id, eg.'2q348ihbfow9lehyr'

They each have multiple attempts at an experimental task.

I now want to re-number all the trials by each participant with a simple number (from 1 upto around 300) and can't work out how to do this.

i know this is very easy!

Answer 1

[Guillaume]

The 1st and 3rd output of unique is what you want. e.g.:

%completely made up demo data. Using a table for neatness. It doesn't matter which form you data comes in
t = table({'2q348ihbfow9lehyr'; '1az3'; '8bq7'; '1az3'; '2q348ihbfow9lehyr'; '1az3'; '5edf'}, [1;10;2;3;5;20;0], 'VariableNames', {'subject', 'testresult'})

[subjects, ~, id] = unique(t.subject)  %get a mapping between subject string and integer id
t.id = id  %optionally add the id the table

[Gloria Estefan]

Thanks Guillaume,

That is very helpful indeed.