[R] [R-pkgs] reshape2 1.1
hadley at rice.edu
Tue Jan 4 15:16:02 CET 2011
Reshape2 is a reboot of the reshape package. It's been over five years
since the first release of the package, and in that time I've learned
a tremendous amount about R programming, and how to work with data in
R. Reshape2 uses that knowledge to make a new package for reshaping
data that is much more focussed and much much faster.
This version improves speed at the cost of functionality, so I have
renamed it to `reshape2` to avoid causing problems for existing users.
Based on user feedback I may reintroduce some of these features.
What's new in `reshape2`:
* considerably faster and more memory efficient thanks to a much better
underlying algorithm that uses the power and speed of subsetting to the
fullest extent, in most cases only making a single copy of the data.
* cast is replaced by two functions depending on the output type: `dcast`
produces data frames, and `acast` produces matrices/arrays.
* multidimensional margins are now possible: `grand_row` and `grand_col` have
been dropped: now the name of the margin refers to the variable that has
its value set to (all).
* some features have been removed such as the `|` cast operator, and the
ability to return multiple values from an aggregation function. I'm
reasonably sure both these operations are better performed by plyr.
* a new cast syntax which allows you to reshape based on functions
of variables (based on the same underlying syntax as plyr):
* better development practices like namespaces and tests.
Initial benchmarking has shown `melt` to be up to 10x faster, pure
reshaping `cast` up to 100x faster, and aggregating `cast()` up to 10x
This work has been generously supported by BD (Becton Dickinson).
* `melt.data.frame` no longer turns characters into factors
* All melt methods gain a `na.rm` and `value.name` arguments - these
previously were only possessed by `melt.data.frame` (Fixes #5)
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
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