类型is/as

is

• is.na
• is.character
• is.ts
• is.numberic
• is.character
• is.vector
• is.matrix
• is.data.frame
• is.factor
• is.logical

as

• as.numberic
• as.matrix
• as.dataframe

which(A==1,arr.ind=T)

which(ll <- c(TRUE, FALSE, TRUE, NA, FALSE, FALSE, TRUE)) #
> 1 3 7

which((1:12)%%2 == 0) # which are even?