在 R 中，几乎is.*我能想到的每个函数都有一个对应的as.*. 有is.na但没有as.na。为什么不，如果这样的功能有意义，你将如何实现？
我有一个x可以是logical、character、 或的向量integer，我想将其转换为具有相同类和长度的向量，但填充了适当的：、、、或。numericcomplexNANA_character_NA_integer_NA_real_NA_complex_
我目前的版本：
as.na <- function(x) {x[] <- NA; x}
为什么不is.na<-按照指示使用?is.na？
> l <- list(integer(10), numeric(10), character(10), logical(10), complex(10))
> str(lapply(l, function(x) {is.na(x) <- seq_along(x); x}))
List of 5
$ : int [1:10] NA NA NA NA NA NA NA NA NA NA
$ : num [1:10] NA NA NA NA NA NA NA NA NA NA
$ : chr [1:10] NA NA NA NA ...
$ : logi [1:10] NA NA NA NA NA NA ...
$ : cplx [1:10] NA NA NA ...
这似乎始终比您的功能快：
as.na <- function(x) {
rep(c(x[0], NA), length(x))
}
（感谢 Joshua Ulrich 指出我的早期版本没有保留类属性。）
为了记录，这里是一些相对时间：
library(rbenchmark)
## The functions
flodel <- function(x) {x[] <- NA; x}
joshU <- function(x) {is.na(x) <- seq_along(x); x}
joshO <- function(x) rep(c(x[0], NA), length(x))
## Some vectors to test them on
int <- 1:1e6
char <- rep(letters[1:10], 1e5)
bool <- rep(c(TRUE, FALSE), 5e5)
benchmark(replications=100, order="relative",
flodel_bool = flodel(bool),
flodel_int = flodel(int),
flodel_char = flodel(char),
joshU_bool = joshU(bool),
joshU_int = joshU(int),
joshU_char = joshU(char),
joshO_bool = joshO(bool),
joshO_int = joshO(int),
joshO_char = joshO(char))[1:6]
# test replications elapsed relative user.self sys.self
# 7 joshO_bool 100 0.46 1.000 0.33 0.14
# 8 joshO_int 100 0.49 1.065 0.31 0.18
# 9 joshO_char 100 1.13 2.457 0.97 0.16
# 1 flodel_bool 100 2.31 5.022 2.01 0.30
# 2 flodel_int 100 2.31 5.022 2.00 0.31
# 3 flodel_char 100 2.64 5.739 2.36 0.28
# 4 joshU_bool 100 3.78 8.217 3.13 0.66
# 5 joshU_int 100 3.95 8.587 3.30 0.64
# 6 joshU_char 100 4.22 9.174 3.70 0.51
该函数不存在，因为它不是类型转换。类型转换会将 1L 更改为 1.0，或将“1”更改为 1L。NA 类型不是从其他类型转换而来的，除非该类型是文本。鉴于只有一种类型可以转换，并且有很多选项可以分配 NA （如在许多其他答案中一样），因此不需要这样的功能。
您获得的每个答案都会将 NA 分配给传递给它的所有内容，但您可能只想有条件地执行此操作。有条件地进行分配或调用小型包装器也没有什么不同。
老问题，但是，怎么样
as.na <- function(obj){
if(is.factor(obj)){
# Special case for factors - any others that need to be handled?
factor(rep(NA, length(obj)), levels = levels(obj))
} else{
objClass <- class(obj)
x <- rep(NA, length(obj))
class(x) <- objClass
x
}
}
对于数据框：
DF <- data.frame(
int = seq(1, 10),
real = seq(1, 10) + 0.1,
char = letters[1:10],
logi = rep(c(TRUE, FALSE), 5),
Date = seq.Date(as.Date("2019-09-03"), by = 1, length.out = 10),
posix = seq.POSIXt(as.POSIXct("2019-09-03 12:00:00"), by = 360, length.out = 10),
stringsAsFactors = FALSE
)
DF$factr <- as.factor(LETTERS[1:10])
str(DF)
'data.frame': 10 obs. of 7 variables:
$ int : int 1 2 3 4 5 6 7 8 9 10
$ real : num 1.1 2.1 3.1 4.1 5.1 6.1 7.1 8.1 9.1 10.1
$ char : chr "a" "b" "c" "d" ...
$ logi : logi TRUE FALSE TRUE FALSE TRUE FALSE ...
$ Date : Date, format: "2019-09-03" "2019-09-04" "2019-09-05" ...
$ posix: POSIXct, format: "2019-09-03 12:00:00" "2019-09-03 12:06:00" "2019-09-03 12:12:00" ...
$ factr: Factor w/ 10 levels "A","B","C","D",..: 1 2 3 4 5 6 7 8 9 10
DF_na <- DF
for(i in colnames(DF_na)){
DF_na[,i] <- as.na(DF_na[,i])
}
str(DF_na)
'data.frame': 10 obs. of 7 variables:
$ int : int NA NA NA NA NA NA NA NA NA NA
$ real : num NA NA NA NA NA NA NA NA NA NA
$ char : chr NA NA NA NA ...
$ logi : logi NA NA NA NA NA NA ...
$ Date : Date, format: NA NA NA ...
$ posix: POSIXct, format: NA NA NA ...
$ factr: Factor w/ 10 levels "A","B","C","D",..: NA NA NA NA NA NA NA NA NA NA
对于数据表：
library(data.table)
DT <- data.table::data.table(
int = seq(1, 10),
real = seq(1, 10) + 0.1,
char = letters[1:10],
logi = rep(c(TRUE, FALSE), 5),
Date = seq.Date(as.Date("2019-09-03"), by = 1, length.out = 10),
posix = seq.POSIXt(as.POSIXct("2019-09-03 12:00:00"), by = 360, length.out = 10),
factr = as.factor(LETTERS[1:10])
)
str(DT)
Classes ‘data.table’ and 'data.frame': 10 obs. of 7 variables:
$ int : int 1 2 3 4 5 6 7 8 9 10
$ real : num 1.1 2.1 3.1 4.1 5.1 6.1 7.1 8.1 9.1 10.1
$ char : chr "a" "b" "c" "d" ...
$ logi : logi TRUE FALSE TRUE FALSE TRUE FALSE ...
$ Date : Date, format: "2019-09-03" "2019-09-04" "2019-09-05" ...
$ posix: POSIXct, format: "2019-09-03 12:00:00" "2019-09-03 12:06:00" "2019-09-03 12:12:00" ...
$ factr: Factor w/ 10 levels "A","B","C","D",..: 1 2 3 4 5 6 7 8 9 10
- attr(*, ".internal.selfref")=<externalptr>
DT_na <-
copy(DT)[, lapply(.SD, as.na)]
str(DT_na)
Classes ‘data.table’ and 'data.frame': 10 obs. of 7 variables:
$ int : int NA NA NA NA NA NA NA NA NA NA
$ real : num NA NA NA NA NA NA NA NA NA NA
$ char : chr NA NA NA NA ...
$ logi : logi NA NA NA NA NA NA ...
$ Date : Date, format: NA NA NA ...
$ posix: POSIXct, format: NA NA NA ...
$ factr: Factor w/ 10 levels "A","B","C","D",..: NA NA NA NA NA NA NA NA NA NA
- attr(*, ".internal.selfref")=<externalptr>