# Swarm Intelligence Algorithms for Feature Selection: A Review
## 6 Applications of Feature Selection with Swarm Intelligence
### Application Areas  
There are a variety of application areas in which the presented algorithms are used for FS. Based on that, we defined the following three main groups of application domains in which the algorithms fall (Figure 8):  
1. Bio-Medical Engineering
2. Electrical and Electronic Engineering
3. Computer Engineering  
The application field regulates all presented research articles and then classifies them based on the used algorithms in Table 3. For the same reason as in Table 2, we excluded the _Group Hunting_ section. \begin{table}
\begin{tabular}{l l c c c} \hline \hline  & **Small** & **Large** & **Mixed** & \(\sum\) \\ \hline \multirow{4}{*}{**Insect**} & ABC [38; 41] & DA [46] & ABC [54] & \\  & BBMO [44; 63] & GSO [50] & FA [42] & \\  & ACO [35] & & ACO [62] & \\  & WSO [73] & & & \\ \hline \hline
**Bacteria** & \multicolumn{2}{c}{BFO and BCO [64]} & \multicolumn{2}{c}{1} \\ \hline
**Bird** & PSO [29; 31] & PSO [66; 74; 75] & PSO [28; 30; 76] & \\  & & [77] & [78] & 10 \\ \hline \multirow{4}{*}{**Mammal**} & GWO [39] & \multicolumn{2}{c}{GWO [34; 40]} \\  & CaTS [65] & \multicolumn{2}{c}{BA [55]} & 6 \\  & & \multicolumn{2}{c}{WOA [67]} & \\ \hline \multirow{2}{*}{**Fish**} & AFSA [51; 52] & \multicolumn{2}{c}{3} \\  & FSA [79] & \multicolumn{2}{c}{} \\ \hline
**Frog** & \multicolumn{2}{c}{SFLA [45]} & 1 \\ \hline
**Other** & \multicolumn{2}{c}{KH [68; 80]} & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Used dataset sizes in evaluating swarm intelligence (SI) for feature selection (FS). Figure 7: Analysis of used datasets in swarm intelligence (SI). Based on the survey, we can state that Bio-Medical Engineering is the most used field for algorithms' testing or applying. Researchers in [58] proposed the Chaos FA algorithm for heart disease prediction; the Bacterial Memetic Algorithm based feature selection for surface EMG-based hand motion recognition in long-term use was suggested by [85]. In [84], the authors tackled FS in Brain-Computer Interfacing (BCI) research with the BFO combined algorithm with learning automata. The proposed algorithm selects a feature subset using discrete wavelength transform, which is applied to break down the EEG data. Microarray gene selection, or expression, is one field in Medical Engineering which is becoming more popular because it plays a crucial part in disease classifications. The researchers in [93] proposed binary GWO for classifying acute leukemia in which the multilayer perceptron neural network was used for fitness function. Some studies [45; 97] use the improved SFLA algorithm on high-dimensional biomedical data for disease diagnosis. Figure 8: Analysis of applications in SI. \begin{table}
\begin{tabular}{l l c c c} \hline \hline  & \begin{tabular}{c} **Bio-Medical** \\ **Engineering** \\ \end{tabular} & \begin{tabular}{c} **Electrical and** \\ **Electronic Engineering** \\ \end{tabular} & \
\begin{tabular}{c} **Computer** \\ **Engineering** \\ \end{tabular} & \(\Sigma\) \\ \hline \multirow{4}{*}{**Insects**} & DA[46] RIO [49] & FA [56] & ABC [33; 41] & \\  & GSO [50] & & FA [53] & \\  & FA [58; 81] & ACO [82] & ACO [83] & \\  & ACO [37; 57] & & & \\ \hline \multirow{2}{*}{**Bacteria**} & BFO [84] & \multirow{2}{*}{
\begin{tabular}{c} BFO and BCO [64] \\ 3 \\ \end{tabular} } \\  & BMA [85] & & & \\ \hline \multirow{2}{*}{**Bird**} & PSO [66; 74; 75; 86] & PSO [87] & PSO [88; 89] & \\  & [76; 90; 91] & & & \\ \hline \multirow{2}{*}{**Mammal**} & GWO [92; 93] & GWO [43] & BA [47] & \\  & GWO [94] & & & \\ \hline \multirow{2}{*}{**Fish**} & FSS [95] & & & \\  & SFLA [97; 45] & & & \\ \hline \multirow{2}{*}{**Frog**} & SFLA [45; 97; 98] & & & \\ \hline \multirow{2}{*}{**Other**} & KH [99] & & & \\  & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Application areas of SI for FS. Image based FS is addressed in [99]. The researchers proposed a method for classifying lung Computed Tomography (CT) images, in which the KH algorithm was used alongside multilayer perceptron neural networks.