2018年3月30日星期五
笔记lecture2(如果乱码 选择file recode UTF-8)
l R语言 lecture2;
l 一、Lecture2中函数类型:1.sqrt()平方根
2. rnorm()随机数字,如rnorm(100)即为随机数字100个
3. Hist()函数,根据数集画出柱状图
4. Args()检查函数功能,比如args(rnorm)
5. Round()将x舍为指定位数的小数,round(x, digits=n)
二、数据类型:
a四种主要类型有logical,numerical,character,integer
b用class()检验数据类型,如class(TRUE)输出结果为“logical”
C.给数字加上L 表明其为整数,如3L ,class(3L)输出为“integer”
D.用 is.integer()检验是否为整数,如is.integer(3),输出为FALSE
E. Character要加引号,且要用半角
F.As.numeric 数据的类型转换 :把它转换为数值型(应用:转换数值 为字符)
三、创建向量vector
A vector is a sequence of data elements of the same data type. A vector can only hold elements of the same type. If you have a vector consisting of numbers and character, R will turn ALL of your values into character data! If you have a vector consisting of numbers and logicals, R will turn ALL of your values into numeric data!(character>numeric>logical)
A. 可以用c()创建向量
B. 用names()函数给向量命名。,将标签附加到函数。例子如下:
suits <- c("spades", "hearts", "diamonds", "clubs")
remain <- c(11, 12, 11, 13)
names(remain) <- suits
remain
此时输remain为:
spades hearts diamonds clubs
11 12 11 13
四、向量的计算
向量的算法对应算数位置
长度不一样的向量,短的向量会循环自动补齐
注意区分大小写,大小写不同代表的值不一样
Mean function—算术平均值
Median ---中位数
Names ---命名
五、# Sequences, Repetition, sorting, and Lengths #
1.输出一到十序列的方法:a. 1:10
b. seq()函数, seq(from=1,to=10)。。。。如果有间隔interval为2,则为seq(from=1,to=10,by2)
2.Repetition重复rep(x = c(3, 6, 8), times = 3)
rep(x = c(3, 6, 8), each = 2)
rep(x = c(3, 6, 8), times = 3, each = 2)
3.Sorting排序 sort(x = c(2.5, -1, -10, 3.44), decreasing = FALSE)
sort(x = c(2.5, -1, -10, 3.44), decreasing = TRUE)
4. length The length function tell us how many elements exist in a vector
如length(x = c(3, 2, 8, 1)),length(5:13)等
六、# Subsetting your Vectors #截取向量
1.Suppose you want to select the first element from this vector, you can use square brackets for this remain[1]
2.选择两个元素 remain[c(4, 1)]
3. Create a vector that contains all the information that's in the `remain` vector, except for the spades count排除某个元素
remain[-1]:
remain[-1]
hearts diamonds clubs
12 11 13
4.可以根据逻辑来选择向量中的元素remain[c(FALSE, TRUE, FALSE, TRUE)]
即选择2,4元素
5.也可以The above expression is the same as the bellowing one
remain[remain > 11]
如果直接remain > 11
结果是remain > 11
spades hearts diamonds clubs
FALSE TRUE FALSE TRUE