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Document how j results are combined with by via rbindlist (issue #7643) #7651

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Document how j results are combined with by via rbindlist (issue #7643) #7651

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Document how j results are combined with by via rbindlist (issue #7643)
mahjabinoyshi Feb 26, 2026
bcbc655
Shorten by doc and remove test per review on #7651
mahjabinoyshi Feb 27, 2026
0a69575
Shorten rbindlist sentence to match reviewer suggestion
mahjabinoyshi Feb 28, 2026
4404909
Restore closing brace on Advanced paragraph per review
mahjabinoyshi Mar 1, 2026
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2 changes: 1 addition & 1 deletion man/data.table.Rd
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Expand Up @@ -97,7 +97,7 @@ data.table(\dots, keep.rownames=FALSE, check.names=FALSE, key=NULL, stringsAsFac

See \href{../doc/datatable-intro.html}{\code{vignette("datatable-intro")}} and \code{example(data.table)}.}

\item{by}{ Column names are seen as if they are variables (as in \code{j} when \code{with=TRUE}). The \code{data.table} is then grouped by the \code{by} and \code{j} is evaluated within each group. The order of the rows within each group is preserved, as is the order of the groups. \code{by} accepts:
\item{by}{ Column names are seen as if they are variables (as in \code{j} when \code{with=TRUE}). The \code{data.table} is then grouped by the \code{by} and \code{j} is evaluated within each group. The order of the rows within each group is preserved, as is the order of the groups. The results are combined using \code{\link{rbindlist}}. \code{by} accepts:

\itemize{
\item A single unquoted column name: e.g., \code{DT[, .(sa=sum(a)), by=x]}
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