R中的一些基础1106

1.R中NA,NaN,Inf代表什么？

NA：缺失数据

NaN：无意义的数，比如sqrt(-2)

Inf：正无穷大

-Inf:负无穷大

2.确定一个数值型vector的第一个最值（最大/最小）的下标：

which.min(x)
which.max(x)

x
numeric (logical, integer or double) vector or an R object for which the internal coercion to double works whose min or max is searched for.

3.对应的，确定一个矩阵每一行最值的下标：

max.col(m, ties.method = c("random", "first", "last"))

m
numerical matrix

ties.method
a character string specifying how ties are handled, "random" by default;

通常第一个参数默认是random，如果是first那么就返回相同最大值中第一列，last与此相反。

4.判断一个逻辑向量中，值为TRUE的下标：

which(x, arr.ind = FALSE, useNames = TRUE)
arrayInd(ind, .dim, .dimnames = NULL, useNames = FALSE)

which(LETTERS == "R")
which(ll <- c(TRUE, FALSE, TRUE, NA, FALSE, FALSE, TRUE)) #>   

转自:https://stat.ethz.ch/R-manual/R-devel/library/base/html/which.html

5.返回输入值中的最大值和最小值

转自：https://stat.ethz.ch/R-manual/R-devel/library/base/html/Extremes.html

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

pmax(..., na.rm = FALSE)
pmin(..., na.rm = FALSE)

pmax.int(..., na.rm = FALSE)
pmin.int(..., na.rm = FALSE)

...
numeric or character arguments (see Note).

na.rm
a logical indicating whether missing values should be removed.

用法:
min(:, pi) #-> one number
pmin(:, pi) #->    numbers