library(data.table)

library(bigmemory)

library(bigalgebra)

options(bigmemory.typecast.warning=FALSE)

for(i in ncol(WOS_table)){

if(is.factor(WOS_table[,i])){

WOS_table[,i] <- as.character(WOS_table[,i])

}

}

max_expected_combinations <- choose(nrow(WOS_table), 2)

number_commun_references <- big.matrix(max_expected_combinations, 1, type = "integer", init = 0, shared = FALSE)

cr_matrix <- big.matrix(nrow(WOS_table), length(unique(unlist(indexed_cr_list)))+1, type = "integer", init = 0, shared = FALSE)

counter <- 0

for(x in 1:length(indexed_cr_list)) {

counter <- counter + 1

cr_matrix[counter,indexed_cr_list[[x]]] <- cr_matrix[counter,indexed_cr_list[[x]]] + 1

}

counter_combinations <- 2:nrow(cr_matrix)

position_counter <- c((nrow(WOS_table)-1):1)

position_counter_2 <- rep(0,length(position_counter)-1)

position_counter_s <- rep(0,length(position_counter)-1)

for(p in 1:length(position_counter)) {

position_counter_2[p] <- sum(position_counter[1:p])

}

position_counter_s <- position_counter_2 + 1

position_counter_s <- append(position_counter_s, 1, 0)

position_counter_s <- position_counter_s[1:(length(position_counter_s)-1)]

cat("\r", " ")

for(rec in 1:length(position_counter_2)) {

number_commun_references[position_counter_s[rec]:position_counter_2[rec],] <- cr_matrix[counter_combinations[rec]:nrow(cr_matrix),] %*% cr_matrix[rec,]

cat("\r", rec, " of ", length(position_counter_2))

}

rec_vector <- WOS_table$UT

source_target_mat <- t(combn(rec_vector, 2))

nref <- as.matrix(number_commun_references)

cocitation_table <- data.table("source" = source_target_mat[,1],

"target" = source_target_mat[,2],

"number_of_references_source" = rep(0,max_expected_combinations),

"number_of_references_target" = rep(0,max_expected_combinations),

"number_of_references_in_commun" = nref)

WOS_table <- as.data.table(WOS_table)

setkey(WOS_table,UT)

setkey(cocitation_table,target)

for(rec in rec_vector) {

cocitation_table[.(rec), number_of_references_target := WOS_table[rec, NR]]

}

setkey(cocitation_table,source)

for(rec in rec_vector) {

cocitation_table[.(rec), number_of_references_source := WOS_table[rec, NR]]

}

cocitation_table <- cocitation_table[number_of_references_in_commun != 0]

WOS_table <- as.data.frame(WOS_table)

cocitation_table <- as.data.frame(cocitation_table)

return(cocitation_table)