在R中快速转换字符* [英] convert character to date *quickly* in R

问题描述

可能重复：

为什么某个字符向量的as.Date慢？

我使用 RMySQL从数据库中读取的大量 data.frame （大约60密耳观察） / code>。日期作为字符（似乎没有办法改变这个），所以我使用 as.Date 将东西转换为日期。然而，这需要非常长的时间，这么多的观察。有没有什么可以做到这样更快？

I have a large data.frame (roughly 60 mil observations) that I read from a database using RMySQL. The dates are brought in as characters (there doesn't seem to be a way to change this) and so I use as.Date to convert things to date. However, this takes an extremely long time witih so many observations. Is there anything one can do to make this faster?

推荐答案

Simon Urbanek的 fasttime 库对于可分解数据时间的一个子集来说非常：

Simon Urbanek's fasttime library is very fast for a subset of parseable datetimes:

R> now <- Sys.time()
R> now
[1] "2012-10-15 10:07:28.981 CDT"
R> fasttime::fastPOSIXct(format(now))
[1] "2012-10-15 05:07:28.980 CDT"
R> as.Date(fasttime::fastPOSIXct(format(now)))
[1] "2012-10-15"
R> 

但是，它只解析ISO格式，并将UTC视为时区。

However, it only parse ISO formats and assume UTC as timezone.

3年半后编辑：有些评论者似乎认为fasttime包很难安装。我不敢苟同。这是（再次）使用 install.r 这只是一个简单的包装器，使用 littler （也作为示例提供）：

Edit after 3 1/2 years: Some commenters appear to think that the fasttime package is difficult to install. I beg to differ. Here is (once again) use install.r which is just a simple wrapper using littler (and also shipped as an example with):

edd@max:~$ install.r fasttime
trying URL 'https://cran.rstudio.com/src/contrib/fasttime_1.0-1.tar.gz'
Content type 'application/x-gzip' length 2646 bytes
==================================================
downloaded 2646 bytes

* installing *source* package ‘fasttime’ ...
** package ‘fasttime’ successfully unpacked and MD5 sums checked
** libs
ccache gcc -I/usr/share/R/include -DNDEBUG      -fpic  -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -D_FORTIFY_SOURCE=2 -g  -O3 -Wall -pipe -pedantic -std=gnu99  -c tparse.c -o tparse.o
ccache gcc -shared -L/usr/lib/R/lib -Wl,-Bsymbolic-functions -Wl,-z,relro -o fasttime.so tparse.o -L/usr/lib/R/lib -lR
installing to /usr/local/lib/R/site-library/fasttime/libs
** R
** preparing package for lazy loading
** help
*** installing help indices
** building package indices
** testing if installed package can be loaded
* DONE (fasttime)

The downloaded source packages are in
        ‘/tmp/downloaded_packages’
edd@max:~$ 

正如你所见，该软件包具有零外部依赖关系，一个源文件，并且没有轻微的挂钩构建。我们还可以看到 fasttime 现在正在进行CRAN，但答案并非如此是写的因此，Windows和OS X二进制文件现在确实存在于该页面，并且即使您不从源代码安装，安装也将像我一样简单。

As you can see, the package has zero external dependencies, one source file and builds without the slightest hitch. We can also see that fasttime is now on CRAN which was not the case when the answer was written. With that, Windows and OS X binaries now do exist at that page and the installation will be as easy as it was for me even when you do not install from source.

这篇关于在R中快速转换字符*的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！