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selection.py: add fitness_greedy param to selDoubleTournament #726

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selection.py: add fitness_greedy param to selDoubleTournament #726

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24 changes: 17 additions & 7 deletions deap/tools/selection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -103,7 +103,7 @@ def selRoulette(individuals, k, fit_attr="fitness"):
return chosen


def selDoubleTournament(individuals, k, fitness_size, parsimony_size, fitness_first, fit_attr="fitness"):
def selDoubleTournament(individuals, k, fitness_size, parsimony_size, fitness_first, fitness_greedy=False, fit_attr="fitness"):
"""Tournament selection which use the size of the individuals in order
to discriminate good solutions. This kind of tournament is obviously
useless with fixed-length representation, but has been shown to
Expand Down Expand Up @@ -138,6 +138,9 @@ def selDoubleTournament(individuals, k, fitness_size, parsimony_size, fitness_fi
(size tournament feeding fitness tournaments with candidates). It has been \
shown that this parameter does not have a significant effect in most cases\
(see [Luke2002fighting]_).
:param fitness_greedy: Set this to True if the size tournament should always \
keep the fitter individual, and only apply size selection when the fitnesses \
are tied.
:param fit_attr: The attribute of individuals to use as selection criterion
:returns: A list of selected individuals.

Expand All @@ -151,14 +154,21 @@ def _sizeTournament(individuals, k, select):
for i in range(k):
# Select two individuals from the population
# The first individual has to be the shortest
prob = parsimony_size / 2.
ind1, ind2 = select(individuals, k=2)

if len(ind1) > len(ind2):
ind1, ind2 = select(individuals, k=2)
f1, f2 = [getattr(ind, fit_attr).values[0] for ind in [ind1, ind2]]
prob = 1.

if f1 == f2 or not fitness_greedy:
prob = parsimony_size / 2.
if len(ind1) > len(ind2):
ind1, ind2 = ind2, ind1
elif len(ind1) == len(ind2):
# random selection in case of a tie
prob = 0.5
elif f2 < f1:
ind1, ind2 = ind2, ind1
elif len(ind1) == len(ind2):
# random selection in case of a tie
prob = 0.5


# Since size1 <= size2 then ind1 is selected
# with a probability prob
Expand Down