I have a data.frame with two columns. One indicating objects, the other one indicates if the objects are within some group. How can I create an adjacency matrix without writing a loop?
data("mtcars")
testdf <- data.frame(names=as.character(row.names(mtcars)[1:5]),
ingroup=0)
set.seed(123)
testdf$ingroup[testdf$names%in%row.names(mtcars)[sample(length(row.names(mtcars)[1:5]), 2)]] <- 1
testdf
names ingroup
1 Mazda RX4 0
2 Mazda RX4 Wag 1
3 Datsun 710 0
4 Hornet 4 Drive 1
5 Hornet Sportabout 0
EDIT: The desired output should be a matrix indicating if objects are within a certain group:
data.frame(x1=c(0,0,0,0,0),
x2=c(0,1,0,0,1),
x3=c(0,0,0,0,0),
x4=c(0,0,0,0,0),
x5=c(0,1,0,0,1))
colnames(output) <- c("Datsun 710", "Hornet 4 Drive", "Hornet Sportabout", "Mazda RX4","Mazda RX4 Wag")
rownames(output) <- c("Datsun 710", "Hornet 4 Drive", "Hornet Sportabout", "Mazda RX4","Mazda RX4 Wag")
output
Datsun 710 Hornet 4 Drive Hornet Sportabout Mazda RX4 Mazda RX4 Wag
Datsun 710 0 0 0 0 0
Hornet 4 Drive 0 1 0 0 1
Hornet Sportabout 0 0 0 0 0
Mazda RX4 0 0 0 0 0
Mazda RX4 Wag 0 1 0 0 1
Thanks, Thomas
You just take the cross product of the ingroup variable:
res <- tcrossprod(testdf$ingroup)
rownames(res) <- testdf$names
colnames(res) <- testdf$names
res
# Mazda RX4 Mazda RX4 Wag Datsun 710 Hornet 4 Drive Hornet Sportabout
# Mazda RX4 0 0 0 0 0
# Mazda RX4 Wag 0 1 0 1 0
# Datsun 710 0 0 0 0 0
# Hornet 4 Drive 0 1 0 1 0
# Hornet Sportabout 0 0 0 0 0