向量的运算

1、计算向量长度：length()

> length(diag(4))  # = 16 (4 x 4)
[1] 16
> length(seq(1, 9, by = pi))
[1] 3

2、求和：sum()

sum(..., na.rm = FALSE)

> sum(1, 2, 3, 4, 5)
[1] 15
> sum(1:5, NA)  # 若向量中含NA，则和为NA
[1] NA
> sum(1:5, NA, na.rm = TRUE)  ## 若向量中含NA，na.rm可计算除NA外的向量之和
[1] 15

3、计算平均值：mean()

mean(x, trim = 0, na.rm = FALSE, ...)

> x <- c(0:10, 50)
> xm <- mean(x)
> c(xm, mean(x, trim = 0.10))  ## mean(x, trim = 0.10) 先把x的最大的10%的数和最小的10%的数去掉，然后剩下的数算平均
[1] 8.75 5.50

4、计算中位数：median()

median(x, na.rm = FALSE, ...)

> median(1:4)
[1] 2.5
> median(c(1:3, 100, 1000))
[1] 3

5、计算最小值：min()、计算最大值：max()

max(..., na.rm = FALSE)
min(..., na.rm = FALSE)

> max(1:10)
[1] 10
> min(1:10)
[1] 1

7、计算方差：sd()

sd(x, na.rm = FALSE)

> sd(1:2)
[1] 0.7071068
> sd(1:2) ^ 2
[1] 0.5