抑制data.table j函数中的输出

Question

我想在一个使用中ccf为一个id变量的不同值绘制一些图.问题是返回一个不符合的值.我不关心返回值,只想看实际情节.一些代码:data.tableRccfdata.table

require(data.table)
x <- data.table(id=rep(1:10, each=10), a=rep(1:10,10), b=rep(10:1,10))
x[,ccf(a,b),by=id]
Error in `[.data.table`(x, , ccf(a, b), by = id) : 
All items in j=list(...) should be atomic vectors or lists. If you are trying something like j=list(.SD,newcol=mean(colA)) then use := by group instead (much quicker), or cbind or merge afterwards.

Answer 1

鉴于此问题:

我不关心返回值,只想看实际情节.

然后 :

x[, {ccf(a,b);NULL}, by=id]