澄清R中的L [英] Clarification of L in R

问题描述

我在R中L的足迹是:

c<-1:10
c
# [1]  1  2  3  4  5  6  7  8  9 10
c[-1]
# [1]  2  3  4  5  6  7  8  9 10
c[-2]
# [1]  1  3  4  5  6  7  8  9 10
c[-1L]
# [1]  2  3  4  5  6  7  8  9 10
c[-2L]
# [1]  1  3  4  5  6  7  8  9 10

我尝试使用?L失败.

x[<n>L]的确是什么?有进一步使用它的例子吗?

What indeed is x[<n>L]? Any example for further usage of it?

推荐答案

此答案是以上评论的摘要.它基本上只是指向各种帮助文本的指针，但是从OP对?L的尝试中可以明显看出，找到相关的帮助文本并不总是那么容易.我期望在?as.integer中找到有关L的信息，但没有.希望这个答案比一堆评论有用.

This answer is a summary of the comments above. It is basically just pointers to various help texts, but as evident from OP's attempt with ?L, it is not always easy to find the relevant help text. I was expecting to find something about L in ?as.integer, but no. Hopefully this answer is more useful than a pile of comments.

• 使用 R语言 定义 您会发现:我们可以使用L后缀来限定任何数字 旨在使其成为一个显式整数"

• 来自?NumericConstants:"[...]所有其他数字常量开始 带有数字或句点，并且可以是十进制或十六进制 常量(可选)，后跟L"

• In the R language definition you will find: "We can use the L suffix to qualify any number with the intent of making it an explicit integer"

• From ?NumericConstants: "[...] All other numeric constants start with a digit or period and are either a decimal or hexadecimal constant optionally followed by L"

"紧随其后的数字常量L被视为 整数(如果可能)(如果包含 .")."

"An numeric constant immediately followed by L is regarded as an integer number when possible (and with a warning if it contains a ".")."

您可以将前缀"0x"与后缀"L"结合使用.

"You can combine the "0x" prefix with the "L" suffix".

有关有关L效率的讨论的主题:

Threads with discussions about the efficiency of L:

R-help上的线程，其他人很难找到有关L的文档，并可能对字母L的原因以及为什么L vs as.integer的效率进行了解释.

Threads on R-help where others have struggled to find documentation about L, with a possible explanation of why the letter L, and why L vs as.integer in terms of efficiency.

1. 10至10升之间的差异

第一位威廉·邓拉普(William Dunlap):

First William Dunlap:

为什么10I不是整数?可能是因为"I"和"l"看起来太相似，也许是因为"i"和"I"听起来太相似了. "L"并不表示"long":整数为4个字节长.

Why not 10I for integer? Perhaps because "I" and "l" look too similar, perhaps because "i" and "I" sound too similar. The "L" does not mean "long": integers are 4 bytes long.

然后布莱恩·里普利(Brian Ripley):

Then Brian Ripley:

实际上是这样的:此表示法起源于16位C语言 整数为16位而long为32位的计算机(R 没有"long"类型).

Actually it does: this notation dates from the C language on 16-bit computers where integers were 16-bits and longs were 32-bit (and R has no 'long' type).

R中这个的作者从未解释过为什么他选择了这种符号，但是 它比as.integer(10)短，并且效率更高，因为强制是 在解析时完成.

The author of this in R never explained why he chose the notation, but it is shorter than as.integer(10), and more efficient as the coercion is done at parse time.

L字
通过基准测试讨论不同情况下的效率.

The L Word
Discussion about the efficiency in different situations, with some benchmarkings.

R历史记录:为什么'L;后缀字符"L"表示整数常量?

更多讨论 此处 .

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