create data

DT<-data.table(ID=1:50, Capacity=sample(100:1000,size=50,replace=F), Code=sample(LETTERS[1:4], 50, replace=T), State=rep(c("Alabama","Indiana","Texas","Nevada"),50))

Simple data.table command

DT[Code=="C",mean(Capacity),State]
DT[Code=="D"]
DT[,mean(Capacity),by=State]
DT[Code=="A", mean(Capacity)]
[1] 614.5714

load data which has 130MB with 1714258 rows of 12 columns

DT<-fread("C:\\Users\\r631758\\Desktop\\r631758\\R codes\\datatable\\GB_full.csv")


Read 43.0% of 1720673 rows
Read 70.9% of 1720673 rows
Read 1720673 rows and 12 (of 12) columns from 0.191 GB file in 00:00:05

subsetting rows

sub_rows<-DT[V4=="England" & V3=="Beswick"]

subsetting columns

ordering columns

dt_order<-DT[order(V4,-V8)]

add a new column

DT[,V_new:=V10+V11]

update row values

delete a column

compute the average

computer the count

setting a key

subsetting England from V4

set multiple keys

for more info: https://cran.r-project.org/web/packages/data.table/vignettes/datatable-intro.html

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