[datatable-help] "ungrouping" a data.table

[statquant3]

dtUngroup <- function(DT){
	colClasses <- lapply(DT,FUN=class)
	listCols <- which(colClasses=='list')
	if(length(listCols)>0){
		nonListCols <- setdiff(colnames(DT),listCols)
		nbListElem <- unlist(DT[,lapply(.SD,FUN=lengths),.SDcols=(listCols[1L])])
		DT1 <- DT[,lapply(.SD,FUN=rep,times=(nbListElem)),.SDcols=(nonListCols)]
		DT1[,(listCols):=DT[,lapply(.SD,FUN=function(x)
do.call('c',x)),.SDcols=(listCols)]]
		return(DT1)
	}
	return(DT)
}

This works... still 20x slower than the equivalent in kdb



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