Data Table in R

Data Table Package in R

library(data.table)

data.table(x = c("A", "B"), y = 1:4)
DT <- data.table(a = c(1L,2L,1L,2L), b = LETTERS[1:4])
target <- data.table(B = c("a", "b", "c", "d", "e", "a", "b", "c", "d", "e"),  val = as.integer(c(6:10, 1:5)))
> X = data.table(grp=c("a","a","b","b","b","c","c"), foo=1:7)
> Y = data.table(c("b","c"), bar=c(4,2))
> DF = data.frame(x=1:3,y=4:6,z=7:9)
> DT = data.table(DF)
> DT = as.data.table(iris)
  print(names(DT))
print(dim(DT))

DT[i, j, by]
DT[.N]
DT[nrow(DT)]
print(DT[c(2,2,3)])
DT[, .(col2, col5)]
dt1[, 'col1', with=FALSE]
dt1[, list(col1)]
DT[, .(Total=sum(A), Mean=mean(C))]
DT[, .(B, C=sum(C))]
dt[, plot(A,C)]
DT[, .(Sum=sum(B), Mean=mean(B)), by=.(A)]
DT[, .(Sum=sum(B), by=.(Grp=A%%2)]
dt[2:4, mean(C), by=A%%2]
DT2[, .(C = tail(C, 2)), by = A]
DT[, .(Count = .N), by = .(Area = 10 * round(Sepal.Length * Sepal.Width / 10))]
dt1[J('1', c('2','3')), ]
dt2[, list(col1=mean(col1), col2sum=sum(col2)), by=list(col3,col4)]

print(DT[,mean(Sepal.Length),by=Species])
print(DT[,mean(Sepal.Length),by=substr(Species,1,1)])
data = fread("bugs.csv")
df = fread("...copy paste data.......", col.names=c("Col1", "Col2"))

tables() ==> Show info for each data.table in memory
keys() ==> Show Keys in data.table
setkey(dt1, col1) ==> Create index for col1 and reorder data according to col1

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