I am newbie to Particle Swarm Optimization. I read research paper on Clustering based on PSO and K-means but I did not found any working example of the same. Any kind of help is much appreciated. Thanks in advance!
I want to perform text document clustering using PSO and K-means in R. I have the basic idea that first PSO will give me the optimised values of the cluster centroids, then I have to use those optimised value of cluster centroids of PSO as the initial cluster centroid for k-means to get cluster of documents.
Below are the codes which describe what I have done so far!
#Import library
library(pdist)
library(hydroPSO)
#Create matrix and suppose it is our document term matrix which we get after
the cleaning of corpus
( In my actual data I have 20 documents with 951 terms i.e., dim(dtm) = 20*951 )
matri <- matrix(data = seq(1, 20, 1), nrow = 4, ncol = 7, byrow = TRUE)
matri
[,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 1 2 3 4 5 6 7
[2,] 8 9 10 11 12 13 14
[3,] 15 16 17 18 19 20 1
[4,] 2 3 4 5 6 7 8
#Initially select first and second row as centroids
cj <- matri[1:2,]
#Calculate Euclidean Distance of each data point from centroids
vm <- as.data.frame(t(as.matrix(pdist(matri, cj))))
vm
V1 V2 V3 V4
1 0.00000 18.52026 34.81379 2.645751
2 18.52026 0.00000 21.51744 15.874508
#Create binary matrix S in which 1 means Instance Ii is allocated to the cluster Cj otherwise 0.
S <- matrix(data = NA, nrow = nrow(vm), ncol = ncol(vm))
for(i in 1:nrow(vm)){
for(j in 1:ncol(vm)){
cd <- which.min(vm[, j])
ifelse(cd==i, S[i,j] <-1, S[i,j] <-0)
}
}
S
[,1] [,2] [,3] [,4]
[1,] 1 0 0 1
[2,] 0 1 1 0
#Apply `hydroPSO()` to get optimised values of centroids.
set.seed(5486)
D <- 4 # Dimension
lower <- rep(0, D)
upper <- rep(10, D)
m_s <- matrix(data = NA, nrow = nrow(S), ncol = ncol(matri))
Fn= function(y) { #Objective Function which has to be minimised
for(j in 1:ncol(matri)){
for(i in 1:nrow(matri)){
for(k in 1:nrow(y)){
for(l in 1:ncol(y)){
m_s[k,] <- colSums(matri[y[k,]==1,])/sum(y[k,])
}
}
}
}
sm <- sum(m_s)/ nrow(S)
return(sm)
}
hh1 <- hydroPSO(S,fn=Fn, lower=lower, upper=upper,
control=list(write2disk=FALSE, npart=3))
But the above hydroPSO() function is not working. It is giving error Error in 1:nrow(y) : argument of length 0. I searched for it but didn't get any solution which works for me.
I also made some changes in my objective function and this time hydroPSO() worked but I guess not correctly. I am passing my initial centroid matrix as a parameter whose dimension is 2*7 but the function returns only 1*7 optimised values. I am not getting its reason.
set.seed(5486)
D <- 7# Dimension
lower <- rep(0, D)
upper <- rep(10, D)
Fn = function(x){
vm <- as.data.frame(t(as.matrix(pdist(matri, x))))
S <- matrix(data = NA, nrow = nrow(vm), ncol = ncol(vm))
for(i in 1:nrow(vm)){
for(j in 1:ncol(vm)){
cd <- which.min(vm[, j])
ifelse(cd==i, S[i,j] <-1, S[i,j] <-0)
}
}
m_s <- matrix(data = NA, nrow = nrow(S), ncol = ncol(matri))
for(j in 1:ncol(matri)){
for(i in 1:nrow(matri)){
for(k in 1:nrow(S)){
for(l in 1:ncol(S)){
m_s[k,] <- colSums(matri[S[k,]==1,])/sum(S[k,])
}
}
}
}
sm <- sum(m_s)/ nrow(S)
return(sm)
}
hh1 <- hydroPSO(cj,fn=Fn, lower=lower, upper=upper,
control=list(write2disk=FALSE, npart=2, K=2))
Output of the above function.
## $par
## Param1 Param2 Param3 Param4 Param5 Param6 Param7
## 8.6996174 2.1952303 5.6903588 0.4471795 3.7103161 1.6605425 8.2717574
##
## $value
## [1] 61.5
##
## $best.particle
## [1] 1
##
## $counts
## function.calls iterations regroupings
## 2000 1000 0
##
## $convergence
## [1] 3
##
## $message
## [1] "Maximum number of iterations reached"
I guess I am passing parameters to the hydroPSO() in a wrong way. Please correct me where I'm doing it wrong.
Thank you very much!
Instead of passing cj to hydroPSO() I used as.vector(t(cj)) in my second approach and it worked fine for me. I got 14 optimised values