任何帮助表示赞赏。 R：创建计算 x 的 sqrt 的函数，如果 x 为负返回 Na

Question

Create a function that, given a numeric value x, calculates the square root of x. If the value contained in x is negative it should return NA.

Answer 1

One possibility would be:

fun <- function(x) x^.5
fun(3)
# [1] 1.732051
fun(-1)
# [1] NaN

If NA needed instead of NaN , use an ifelse .

fun2 <- function(x) ifelse(x < 0, NA, x^.5)
fun2(-1)
# [1] NA
fun2(3)
# [1] 1.732051
fun2(c(-1, 3))
# [1]       NA 1.732051

Answer 2

You can try ifelse to define your vectorized custom function f , eg,

f <- Vectorize(function(x) ifelse(x>=0,sqrt(x),NA))

or

f <- function(x) suppressWarnings(ifelse(x>=0,sqrt(x),NA))

Example

> f(c(-1,0,1,2,3))
[1]       NA 0.000000 1.000000 1.414214 1.732051