像 R 的 is.na 函数一样在 Julia 中查找缺失值 [英] Find the missing values in Julia like R's is.na function

问题描述

Julia 1.0.0 documentation 说明了 Julia 和 R 中的缺失值:

The Julia 1.0.0 documentation says this about missing values in Julia and R:

在 Julia 中，缺失值由缺失对象而不是 NA 表示.使用 ismissing(x) 代替 isna(x).skipmissing 函数通常用于代替 na.rm=TRUE(尽管在某些特定情况下，函数采用 skipmissing 参数).

In Julia, missing values are represented by the missing object rather than by NA. Use ismissing(x) instead of isna(x). The skipmissing function is generally used instead of na.rm=TRUE (though in some particular cases functions take a skipmissing argument).

这是我想在 Julia 中复制的 R 示例代码:

Here is example code in R that I would like to duplicate in Julia:

> v = c(1, 2, NA, 4)
> is.na(v)
[1] FALSE FALSE  TRUE FALSE

(首先请注意，is.na 是 R 函数的正确拼写，而不是上面引用中显示的 isna，但这不是我的意思.)

(First note that is.na is the R function's correct spelling, not isna as shown in the quote above, but that is not my point.)

如果我按照文档的建议在 Julia 中使用 ismissing，我会得到与 R 中不同类型的结果.

If I follow the documentation's suggestion to use ismissing in Julia, I get a different type of result than in R.

julia> v = [1, 2, missing, 4]
4-element Array{Union{Missing, Int64},1}:
 1
 2
  missing
 4

# Note that based on R, I was expecting: `false false true false` 
# though obviously in a different output format.
julia> ismissing(v)
false

要复制 R 代码，我似乎必须执行以下操作:

To duplicate the R code, I seem to have to do something like:

julia> [ismissing(x) for x in v]
4-element Array{Bool,1}:
 false
 false
  true
 false

这行得通，但它不如 R 中的 is.na 简洁.也许我遗漏了一些东西.

That works, but it is not as succinct as is.na in R. Maybe I am missing something.

我也试过了:

julia> ismissing(v[:])
false

julia> ismissing(v[1:end])
false

有什么建议吗?

推荐答案

你可以用广播ismissing.:

You can broadcast ismissing with .:

julia> v = [1, 2, missing, 4]
4-element Array{Union{Missing, Int64},1}:
 1
 2
  missing
 4

julia> ismissing.(v)
4-element BitArray{1}:
 false
 false
  true
 false

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