README.md
1# reshape2
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4[](https://github.com/hadley/reshape/actions)
5[](https://codecov.io/gh/hadley/reshape?branch=master)
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7
8## Status
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10[](https://img.shields.io/badge/lifecycle-retired-orange.svg)
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12reshape2 is retired: only changes necessary to keep it on CRAN will be made. We recommend using [tidyr](http://tidyr.tidyverse.org/) instead.
13
14## Introduction
15
16Reshape2 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.
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18This 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.
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20What's new in `reshape2`:
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22 * considerably faster and more memory efficient thanks to a much better
23 underlying algorithm that uses the power and speed of subsetting to the
24 fullest extent, in most cases only making a single copy of the data.
25
26 * cast is replaced by two functions depending on the output type: `dcast`
27 produces data frames, and `acast` produces matrices/arrays.
28
29 * multidimensional margins are now possible: `grand_row` and `grand_col` have
30 been dropped: now the name of the margin refers to the variable that has
31 its value set to (all).
32
33 * some features have been removed such as the `|` cast operator, and the
34 ability to return multiple values from an aggregation function. I'm
35 reasonably sure both these operations are better performed by plyr.
36
37 * a new cast syntax which allows you to reshape based on functions
38 of variables (based on the same underlying syntax as plyr):
39
40 * better development practices like namespaces and tests.
41
42 * the function `melt` now names the columns of its returned data frame `Var1`, `Var2`, ..., `VarN` instead of `X1`, `X2`, ..., `XN`.
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44 * the argument `variable.name` of `melt` replaces the old argument `variable_name`.
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46Initial benchmarking has shown `melt` to be up to 10x faster, pure reshaping `cast` up to 100x faster, and aggregating `cast()` up to 10x faster.
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48This work has been generously supported by BD (Becton Dickinson).
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