为什么将数字转换为字符会更改数字? [英] Why can converting numbers to characters change the numbers?

问题描述

我想这与R的数据结构有关，答案很快，但是我还没有找到一个答案，

I imagine this has to do with R's data structures and the answer will be quick, but I haven't yet found one so here goes:

as.character(9875987598759875)
[1] "9875987598759876"

library(crayon)
chr(9875987598759875)
[1] "9875987598759876"

toString(9875987598759875)
[1] "9875987598759876"

有什么作用?我应该如何更安全地进行此转换?

What gives? How should I be making this conversion more safely?

推荐答案

.Machine $ integer.max 表示R可以存储的最大整数是2147483647(可以想象在不同平台上会有所不同，但这是不太可能的).大于该数字的任何数字都会自动转换为浮点，并伴有不精确/舍入错误.(与Python不同，Python昂贵但不可思议地根据需要将整数变量转换为任意长度的表示形式.)

.Machine$integer.max indicates that the largest integer R can store is 2147483647 (this could conceivably vary across platforms, but it's very unlikely to). Any number larger than that is automatically converted to floating point, with the attendant imprecision/round-off error. (Unlike in Python, which expensively but magically converts integer variables to an arbitrary-length representation as necessary.)

如果安装了 bit64 程序包，则可以使用64位整数，其准确度最高(大概)

If you install the bit64 package you can use 64-bit integers, with (presumably) exactness up to

print(2^63-1,digits=22)
[1] 9223372036854775808

如果您开始使用字符串，则可以安全地往返转换为 integer64 并返回:

If you start with a character string, you can safely do round-trip conversion to integer64 and back:

library(bit64)
cc <- "9875987598759875"
x <- as.integer64(cc)
identical(cc,as.character(x))
## [1] TRUE

但是，通常，一旦您将数字读入R作为常规数字，就为时已晚.您可以将 colClasses =" integer64" 与 read.table()/ read.csv()/etc一起使用.以 integer64 的形式读取值；我相信 readr 和 data.table 的文件读取功能也具有integer64处理功能.

However, typically once you've read a number into R as a regular number it's too late. You can use colClasses="integer64" with read.table()/read.csv()/etc. to read values in as integer64; I believe the file-reading functions from readr and data.table also have integer64-handling capabilities.

对于许多应用程序，如果您实际上并不打算使用这些数字字符串进行任何数值运算，那么首先确保将它们导入为 character 是最安全，最简单的方法...

For many applications, if you're not actually planning on doing anything numerical with these digit-strings, it's safest and easiest to make sure you import them as character in the first place ...

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