CODEWITHSUNDEEP
rdata.table
Manoj
Manoj

Reputation: 225

Cartesian join in data.table

I am trying to do a full Cartesian join using data.table but with little luck.

Code: 

a = data.table(dt=c(20131017,20131018))
 setkey(a,dt)

 b = data.table(ticker=c("ABC","DEF","XYZ"),ind=c("MISC1","MISC2","MISC3"))
 setkey(b,ticker)

Expected output: 

merge(data.frame(a),data.frame(b),all.x=TRUE,all.y=TRUE)

I have tried merge(a,b,allow.cartesian=TRUE) but it gives me following error - "Error in merge.data.table(a, b, allow.cartesian = TRUE) : A non-empty vector of column names forbyis required."

I am using "R version 3.0.1 (2013-05-16)" with latest data.table packages. Any help would be greatly appreciated!

Regards

Upvotes: 13

Views: 6481

Answers (2)

BrodieG
BrodieG

Reputation: 52687

Expanding on @Codoremifa:

> dt <- c(20131017,20131018)
> b <- data.table(ticker=c("ABC","DEF","XYZ"), ind=c("MISC1","MISC2","MISC3"), key="ticker")
> b[CJ(ticker=ticker, dt=dt)][, c(3, 1, 2)]
         dt ticker   ind
1: 20131017    ABC MISC1
2: 20131018    ABC MISC1
3: 20131017    DEF MISC2
4: 20131018    DEF MISC2
5: 20131017    XYZ MISC3
6: 20131018    XYZ MISC3

Would be nicer if a single command would do it, but this is relatively straightforward.

Upvotes: 0

Se&#241;or O
Se&#241;or O

Reputation: 17432

I think a better solution is:

a[,as.list(b),by=dt]

         dt ticker   ind
1: 20131017    ABC MISC1
2: 20131017    DEF MISC2
3: 20131017    XYZ MISC3
4: 20131018    ABC MISC1
5: 20131018    DEF MISC2
6: 20131018    XYZ MISC3

Upvotes: 26

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