R 是否可以返回不带j的data.table?
是否有方法返回不带任何j列的R 是否可以返回不带j的data.table?,r,data.table,R,Data.table,是否有方法返回不带任何j列的数据表 很多时候,我只是想要一个键或一组键的独特组合 library(data.table) ## Warpbreaks data wb <- as.data.table(warpbreaks) ## Say I just want the summary of wool / tension combos ## I would like to do one of these, but neither works wb[ , j = NULL, keyby =
数据表
很多时候,我只是想要一个键或一组键的独特组合
library(data.table)
## Warpbreaks data
wb <- as.data.table(warpbreaks)
## Say I just want the summary of wool / tension combos
## I would like to do one of these, but neither works
wb[ , j = NULL, keyby = list(wool, tension)] ## <--- Seems legit
wb[keyby = list(wool, tension)] ## <--- Even better!
## This works, but is two steps:
subset(wb[ , .N, keyby=list(wool, tension)], select=-N)
## This almost works, but there is no key
unique(wb[ , list(wool, tension)])
库(data.table)
##翘曲数据
wb是的,在这种情况下,我几乎总是使用.N
,然后保留它(因为它相当无害)。我猜惯用的删除方法是像wb[,.N,keyby=(wool,tension)][,!“N”,with=FALSE]
而不是子集。相关的FR在这里:与@MichaelChirico或setkey(unique(wb[,(wool,tension)])
相关,而不是重新键入名称。@Frank对你来说更快的是wb[,TRUE,keyby=(wool,tension)],!“V1”,with=FALSE]
@MichaelChirico甚至更快的将通过引用删除V1