reshape2 is superseded: only changes necessary to keep it on CRAN will be made. We recommend using tidyr instead.
Reshape2 is a reboot of the reshape package. It's been over five years since the first release of reshape, 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 focused 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
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:
dcastproduces data frames, and
multidimensional margins are now possible:
grand_colhave 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.
meltnow names the columns of its returned data frame
meltreplaces the old argument
Initial benchmarking has shown
melt to be up to 10x faster, pure reshaping
cast up to 100x faster, and aggregating
cast() up to 10x faster.
This work has been generously supported by BD (Becton Dickinson).