Github user sun-rui commented on the pull request:
https://github.com/apache/spark/pull/9193#issuecomment-151055969
@shivaram, [R lag
function](https://stat.ethz.ch/R-manual/R-devel/library/stats/html/lag.html) is
for time series objects, which is irrelevant to the lead/lag here in SQL window
functions.
There are some functions in dplyr package mimicing SQL window functions,
including lead and lag. Refer to
https://cran.r-project.org/web/packages/dplyr/vignettes/window-functions.html
and https://cran.r-project.org/web/packages/dplyr/dplyr.pdf. But a quick glance
at these functions shows that they are working on vectors (for example, lag
right shifts a vector by offset), so the semantic of them are different from
those in Spark.
So for now I won't change this PR.
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