[datatable-help] v1.7.3 submitted to CRAN

[Matthew Dowle]

NEW FEATURES

o   data.table now over-allocates its vector of column pointer slots
    (100 by default). This allows := to add columns fully by
    reference as suggested by Muhammad Waliji, #1646. When the 100
    slots are used up, more space is automatically allocated.
        
    Over allocation has negligible overhead. It's just the vector
    of column pointers, not the columns themselves.
        
o   New function alloc.col() pre-allocates column slots. Use
    this before a loop to add many more than 100 columns, for example,
    to avoid the warning as data.table grows its column pointer vector
    every additional 100 columns; e.g.,
        alloc.col(DT,10000)  # reserve 10,000 column slots
       
o   New function truelength() returns the number of column pointer
    slots allocated, always >= length().
        
o   New option 'datatable.nomatch' allows the default for nomatch
    to be changed from NA to 0, as wished for by Branson Owen.
       
o   cbind(DT,...) now retains DT's key, as wished for by Chris Neff
    and partly implementing FR#295.
        
BUG FIXES

o   Assignment to factor columns (using :=, [<- or $<-) could cause
    'variable not found' errors and a seg fault in some circumstances
    due to a new feature in v1.7.0: "Factor columns on LHS of :=, [<-
    and $<- can now be assigned new levels", fixing #1664. Thanks to
    Daniele Signori for reporting.
        
o   DT[i,j]<-value no longer crashes when j is a factor column and value
    is numeric, fixing #1656.
        
o   An unnecessarily strict machine tolerance test failed CRAN checks
    on Mac preventing v1.7.2 availability for Mac (only).

USER VISIBLE CHANGES

o   := now has its own help page in addition to the examples  
    in ?data.table, see help(":=").
        
o   The error message from X[Y] when X is unkeyed has been lengthened to
    including advice to call setkey first and see ?setkey. Thanks to a
    comment by ilprincipe on Stack Overflow.
        
o   Deleting a missing column is now a warning rather than error. Thanks
    to Chris Neff for reporting, #1642.