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NewStarCTF 2023 公开赛道 Web week1-week2

半秋L 2024-11-06 阅读 97

文章目录


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} 1×31
    • 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)
# %/% 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。
# %/%%% 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.

6 > 5
6 < 5
6 >= 7

3、Logical operators

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

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

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

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
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
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?

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

Getting rid of variables:

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

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