Question

I have a letter trigram table that associates a probability with each trigram of letters, such as ‘thr’. I am not sure what the best way would be to represent such a table in octave, so that the look-ups are efficient.

Any suggestions?

Answer 1

You could use an associative-array-like data structure, aptly named struct().

% Create a new struct
trigrams = struct();

% Add an item explicitly, by using the format 'struct.key',
% where 'key' can be an arbitrary key
trigrams.length = 0;

trigrams.thr = 0.02;
trigrams.length += 1;

% Use setfield() when you don't know the key beforehand (e.g. if you're reading
% the values from a file, etc.)
trigramkey = 'hi';

trigrams = setfield(trigrams, trigramkey, 0.0007);
trigrams.length += 1;

% Likewise, use getfield() when you need a value dynamically
workingprob = getfield(trigrams, trigramkey);

% You can also check the existence of a key
hi_exists = isfield(trigrams, 'hi');

% By the way, you don't actually have to track the length like I've been doing
trigramlength = length(fieldnames(trigrams));

Note that the setfield() function is not in-place; it returns a new struct.