data.frame vs data.table examples


data(Titanic)

# The data is a four dimensional array. 
# Let's melt & recast it into a data.table
Tit <- melt(Titanic)   
Tit <- dcast(Tit, Class+Age+Sex~Survived)

# Make into a data.table for ease of coding
keys <- c("Class", "Age", "Sex")
Tit  <- data.table(Tit, key=keys)

# and a DF copy as well
TitDF <- as.data.frame(Tit)



# Out of curiosity, let's see how many lived/died per class

Tit[, lapply(list(Yes=Yes, No=No), sum), by=Class]
Tit[, lapply(.SD, sum), by=Class, .SDcols=c("No","Yes")]

Tit[, list(Yes=sum(Yes), No=sum(No)), by=Class]


sapply(TitDF[, c("No", "Yes")], by, TitDF$Class, sum)