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Copyright Tristan Aubrey-Jones April 2007.
function result = calculateProb(sample, conds, given)
% CALCULATEPROB calculates the probability of the
% conditions conds occuring for all cases where given occurs.
%
% The parameters 'conds' and 'given' are matrices where each row
% is a condition. Each condition is a two column row vector where
% the left value cond(1) is the column index of the variable in
% the event, and the right value cond(2) is the value that it should
% take for the event to be true.
%
% e.g. calculateProb([1 1; 1 0; 1 0], [2 1], []) = 1/3;
% calculateProb([1 1; 1 0; 1 0], [2 1], [2 1]) = 1;
% calculateProb([1 1; 1 0; 1 0], [2 1], [1 1]) = 1;
sz = size(sample);
cz = size(conds);
gz = size(given);
tot = 0.0;
count = 0;
% for all events in sample
for i = 1:sz(1)
% check if all given conditions apply
alltrue = 1;
for ci = 1:gz(1)
% check current condition
c = given(ci,1:gz(2));
if sample(i, c(1)) ~= c(2)
alltrue = 0;
break;
end
end
% if given true
if alltrue == 1
% increment "out of" count
count = count + 1;
% check if all conditions apply
alltrue = 1;
for ci = 1:cz(1)
% check current condition
c = conds(ci, 1:cz(2));
if sample(i, c(1)) ~= c(2)
alltrue = 0;
break;
end
end
% if conditions hold add to
if alltrue == 1
tot = tot + 1;
end
end
end
% return probability of conds occuring given that
% given already has
if count > 0
result = tot / count;
else
% impossible
result = 0;
end