50:6 Y. Xue et al.
to describe the probability of a strategy. They compared their SLPSO with eight PSO variants on
26 numerical optimization problems with dierent characteristics and an economic load dispatch
problem in power systems. Their results indicate that SLPSO can update the best solution records.
In recent years, Xue et al. (2014b, 2017) proposed some improved self-adaptive EC techniques to
solve the continuous and discrete optimization problems.
Recently, the EC methods with self-adaptive mechanisms have been proposed to solve large-
scale continuous optimization problems, and the experimental results show that these algorithms
have obvious advantages on the continuous numerical optimization problems with high dimen-
sionality (Xue et al. 2014b). However, to our best knowledge, though EC methods with self-adaptive
mechanisms have been employed for solving large-scale feature selection in clustering (Bharti and
Singh 2016), they have not been tried for solving feature selection problems in classication, not to
mention large-scale feature selection in classication. In this article, we investigate a self-adaptive
PSO algorithm to see whether it can achieve good performance for feature selection in classica-
tion, especially for large-scale feature selection in classication.
3 SELF-ADAPTIVE PARTICLE SWARM OPTIMIZATION FOR FEATURE SELECTION
3.1 Representation of Solutions
There are several representation schemes for feature selection in the literature (Xue et al. 2016).
In this article, feature selection is transformed into a “0” and “1” combinatorial optimization prob-
lem,inthesamemannerasthatin(Xueetal.2014a). Thus, the representation of a solution is a
binary string. This string has D dimensions, where D means the total number of features. We use
continuous encoding in PSO, and the range of each dimension of the position vector is limited in
[0, 1]. To transfer a continuous position vector to a binary string, a threshold θ is set in advance.
If the value of the dth dimension of the position is greater than θ, the corresponding value in the
binary vector is set to 1, which represents that the dth feature is selected. Otherwise, the value in
the binary vector is set to 0, which represents that the dth feature is not selected.
3.2 Methods for Designing Strategy Pool
Dierent from the other variant algorithms of PSO that use only one CSGS to generate new parti-
cles, the SaPSO algorithm uses multiple CSGSs to generate new particles. In the SaPSO algorithm,
the multiple CSGSs are maintained in a specic component that is termed as strategy pool. In
order to design the strategy pool for the SaPSO, we have rstly implemented 25 CSGSs that are
commonly used and representative CSGSs in the literature about PSO (The detailed information
of the 25 CSGSs can be seen in the complementary materials). The strategy pool is not constitute
of all the 25 CSGS, i.e., only the suitable CSGSs from the 25 CSGSs are put in the strategy pool. In
this subsection, a method for selecting CSGSs is introduced.
The choice of CSGSs to form the strategy pool has two aspects to consider. (1) How many CSGSs
should be selected to form the pool? (2) Which CSGSs should be selected? There is a basic question
here, i.e., how to identify which CSGSs are eective? We can identify which CSGSs are eective
if there are only one dataset. However, there are a large number of datasets, and we expect the
CSGSs can perform well on the large-scale datasets. The only information that can be obtained is
the performance of the CSGSs on each dataset by doing experiments. Hence, we need a method to
comprehensively evaluate the performance of the CSGSs.
Analytic hierarchy process (AHP) is a famous multicriteria decision making technique (Aguaron
et al. 2016; Saaty 1990). The main characteristics of this approach are as follows: the modeling of
the problem using a hierarchical structure that reects all the relevant aspects of the problem; the
use of pairwise comparisons to incorporate the preferences of decision makers; the derivation of
ACM Transactions on Knowledge Discovery from Data, Vol. 13, No. 5, Article 50. Publication date: September 2019.