R语言笔记（一）

文章目录

[一、R objects](#一、R objects)
[二、Types of data](#二、Types of data)
三、Operators
- 1、Operators
- [2、Comparison operators](#2、Comparison operators)
- [3、Logical operators](#3、Logical operators)
[四、Check types of data objects](#四、Check types of data objects)
[五、Convertion between data objects](#五、Convertion between data objects)
[六、R workspace](#六、R workspace)

一、R objects

Two basic types of things/objects: data and functions

Data : things like 6, "six", 6.000 6.000 6.000, and [ 6 6 6 6 6 6 ] \left[ \begin{array}{ccc} 6 & 6 & 6 \\ 6 & 6 & 6\end{array}\right] [666666]
Functions : things like log, + (takes two arguments), < (two), sum (multiple), and mean (one)

二、Types of data

Booleans
Integers
Characters
Floating point numbers : an integer times a positive integer to the power of an integer, as in 3 × 1 0 6 3 \times 10^6 3×106 or 1 × 3 − 1 1 \times 3^{-1} 1×3−1
- Double precision: 64 bits (8 bytes); Single precision: 32 bits (4 bytes)
Missing or ill-defined values : NA, NaN, etc.

三、Operators

1、Operators

Unary : take just one argument. E.g., - for arithmetic negation, ! for Boolean negation
Binary : take two arguments. E.g., +, -, *, and / (though this is only a partial operator). Also, %% (for mod), and ^ (again partial)

一元运算符：只接受一个参数。例如，负号（-）用于算术取反，感叹号（!）用于布尔取反。

二元运算符：接受两个参数。例如，加号（+）、减号（-）、乘号（*）和除号（/）（尽管除号只是部分运算符）。还有求余运算符（%%），以及幂运算（^）（同样是部分运算符）。

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# %/% 执行整除运算，即只保留商的整数部分，舍弃余数。
# %% 是取模运算符，它返回除法后的余数。
# %/% 和 %% 常配合使用来获取整数商和余数。

10 / 3   # 结果是 3.333333
10 %/% 3 # 结果是 3（商的整数部分）
10 %% 3  # 结果是 1（余数）

2、Comparison operators

These are also binary operators; they take two objects, and give back a Boolean.

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6 > 5
6 < 5
6 >= 7

3、Logical operators

These basic ones are & (and) and | (or).

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(5 > 7) & (6 * 7 == 42)
## [1] FALSE

(5 > 7) | (6 * 7 == 42)
## [1] TRUE

Note: The double forms && and || are different!

四、Check types of data objects

The typeof() function returns the data type
is.x() functions return Boolean values indicating whether the argument is of type x

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typeof(6)
## [1] "double"
is.double(7)
## [1] TRUE
## 解释：在 R 语言中，数字的默认类型是 双精度浮点数（double）。

is.na(7)
## [1] FALSE
is.na(7/0)
## [1] FALSE
## 解释：跟数学里不同，7/0 = Inf  

is.na(0/0)
## [1] TRUE

五、Convertion between data objects

as.x() (tries to) "cast" its argument to type x, to translate it sensibly into such a value

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as.character(5/6)
## [1] "0.833333333333333"

as.numeric(as.character(5/6))
## [1] 0.8333333

6 * as.numeric(as.character(5/6))
## [1] 5

5/6 == as.numeric(as.character(5/6))
## [1] FALSE

六、R workspace

Where do the variables live?

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ls()
## [1] "approx.pi" "circumference" "diameter"

Getting rid of variables:

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rm("circumference")
ls()
## [1] "approx.pi" "diameter"

rm(list=ls()) # Be warned! This erases everything
ls()
## character(0)