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
判断是否存在nan值
is.na(x)#是否存在nan anyNA(x) sum(is.na(x))#存在几个nan值
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)) #> 1 3 7
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(5:1, pi) #-> one number pmin(5:1, pi) #-> 5 numbers