function [total,unigram,bigram] = tally(text)
% [TOTAL,UNIGRAM,BIGRAM] = TALLY(TEXT): compute TOTAL tallies and
% UNIGRAM and BIGRAM frequencies (fractions) of string TEXT or the open file
% with file id TEXT

    fid = -1; % file id of file, if any: start by assuming TEXT is a string
    line = text; % next line of text to process
    go = 1; % keep reading? 
    if ~ischar(text)
        fid = text;
        fprintf('reading %s...', fopen(fid));
        line = fgetl(fid);
    	go = ischar(line);
    end

    % while have more text to process, add up bigram tallies
    	bi = sparse(27,27); % bigram tallies so far
    	while go
    	    line = lower(line) - 'a' + 2; % +2 because space ' ' is at index 1
    	    line (line < 1 | line > 27) = 1; % convert non-letters to space
    	    bi = bi + sparse([1 line], [line 1], 1, 27, 27);
    	    go = fid > 0; % if have a file, then read its next line of text
    	    if go
    		line = fgetl(fid);
    		go = ischar(line);
    	    end
    	end
    
    if fid>0, fclose(fid); end % if processed a file, then close it 

    % compute requested frequencies
        bi(1,1) = 0; % delete double spaces
        bigram = full(bi);
        unigram = sum(bigram);
        total = sum(unigram);
        bigram = bigram/total;
        unigram = unigram/total;

    fprintf('read %d characters\n', total); % print stats about processed text