Extract and collapse non-missing elements by row in the data.table - r

Question

I would like to extract all unique non missing elements in a row and then collapse them using &&&&. Here comes a small example:
#Load needed libraries:
library(data.table)
#Generate the data:
set.seed(1)
n_rows<-10
#Define function to apply to rows:
function_non_missing<-function(x){
x<-x[!is.na(x)]
x<-x[x!="NA"]
x<-unique(x[order(x)])
paste(x,collapse="&&&&")
}
data<-data.table(
a=sample(c(1,2,NA,NA),n_rows,replace=TRUE),
b=sample(c(1,2,NA,NA),n_rows,replace=TRUE),
c=sample(c(1,2,NA,NA),n_rows,replace=TRUE)
)
> data
a b c
1: 1 NA 1
2: NA NA NA
3: NA 1 1
4: 1 1 1
5: 2 1 1
6: 1 2 1
7: NA 2 2
8: NA 2 1
9: 2 2 1
10: 2 NA 2
#Obtain results
data[,paste(.SD),by=1:nrow(data)][,function_non_missing(V1),by=nrow]
nrow V1
1: 1 1
2: 2
3: 3 1
4: 4 1
5: 5 1&&&&2
6: 6 1&&&&2
7: 7 2
8: 8 1&&&&2
9: 9 1&&&&2
10: 10 2
The above code looks very convoluted and I believe there might be better solutions.

Answer 1

Using melt() / dcast():
data[, row := .I
][, melt(.SD, id.vars = "row")
][order(row, value), paste0(unique(value[!is.na(value)]), collapse = "&&&"), by = row]
row V1
1: 1 1
2: 2
3: 3 1
4: 4 1
5: 5 1&&&2
6: 6 1&&&2
7: 7 2
8: 8 1&&&2
9: 9 1&&&2
10: 10 2
Alterntively using your original function:
data[, function_non_missing(unlist(.SD)), by = 1:nrow(data)]
nrow V1
1: 1 1
2: 2
3: 3 2
4: 4 1&&&&2
5: 5 1&&&&2
6: 6 1&&&&2
7: 7 1
8: 8 2
9: 9 1&&&&2
10: 10 1&&&&2

Answer 2

Probably using apply?
library(data.table)
data[, col := apply(.SD, 1, function(x)
paste(sort(unique(na.omit(x))), collapse = "&&&"))]
data
# a b c col
# 1: 1 NA 1 1
# 2: NA NA NA
# 3: NA 1 1 1
# 4: 1 1 1 1
# 5: 2 1 1 1&&&2
# 6: 1 2 1 1&&&2
# 7: NA 2 2 2
# 8: NA 2 1 1&&&2
# 9: 2 2 1 1&&&2
#10: 2 NA 2 2