[datatable-help] v1.6.1 has just been submitted to CRAN

[Matthew Dowle]

NEW FEATURES

   o    j's environment is now consistently reused so
        that local variables may be set which persist
        from group to group; e.g., incrementing a group
        counter :
            DT[,list(z,groupInd<-groupInd+1),by=x]
        Thanks for Andreas Borg for reporting.

   o    A new symbol .BY is now available to j, containing 1 row
        of the current 'by' variables, type list. 'by' variables
        may also be used by name, and are now length 1 too. This
        implements FR#1313. FAQ 2.10 has been updated accordingly.
        Some examples :
            DT[,sum(x)*.BY[[1]],by=eval(byexp)]
            DT[,sum(x)*mylookuptable[J(y),z],by=y]
            DT[,list(sum(unlist(.BY)),sum(z)),by=list(x,y%%2)]

   o    i may now be type list, and works the same as when i
        is type data.table. This saves needing J() in as many
        situations and may be a little more efficient. One
        application is using .BY directly in j to join to a
        relatively small lookup table, once per group, for space
        and time efficiency. For example :
            DT[,list(GROUPDATA[.BY]$name,sum(v)),by=grp]


BUG FIXES

   o    A 'by' character vector of column names now
        works when there are less rows than columns; e.g.,
            DT[,sum(x),by=key(DT)) where nrow(DT)==1.
        Many thanks to Andreas Borg for report, proposed
        fix and tests.
        
   o    Zero length columns in j no longer cause a crash in
        some circumstances. Empty columns are filled with NA
        to match the length of the longest column in j.
        Thanks to Johann Hibschman for bug report #1431.
        
   o    unique.data.table now calls the same internal code
        (in C) that grouping calls. This fixes a bug when
        unique is called directly by user, and, NA exist
        in the key (which might be quite rare). Thanks to
        Damian Betebenner for bug report. unique should also
        now be faster.
        
   o    Variables in calling scope can now be used in j when
        i is logical or integer, fixing bug #1421.

        
USER-VISIBLE CHANGES

    o   ?data.table now documents that logical i is not quite
        the same as i in [.data.frame. NA are treated as FALSE,
        and DT[NA] returns 1 row of NA, unlike [.data.frame.
        Three points have been added to FAQ 2.17. Thanks to
        Johann Hibschman for highlighting.
        
    o   Startup banner now uses packageStartupMessage() so the
        banner can be suppressed by those annoyed by banners,
        whilst still being helpful to new users.