Update README for Julia 1.0 (#103)

README.md

@@ -1,33 +1,32 @@
+# Missings.jl
 
-# Missings
-
-*A missing value representation for Julia for databases and statistics*
-
-| **PackageEvaluator**                                            | **Build Status**                                                                                |
-|:---------------------------------------------------------------:|:-----------------------------------------------------------------------------------------------:|
-|[![][pkg-0.6-img]][pkg-0.6-url] | [![][travis-img]][travis-url] [![][appveyor-img]][appveyor-url] [![][codecov-img]][codecov-url] |
+*Convenience functions for working with missing values in Julia*
 
+[![][travis-img]][travis-url] [![][appveyor-img]][appveyor-url] [![][codecov-img]][codecov-url]
 
 ## Installation
 
-The package is registered in `METADATA.jl` and so can be installed with `Pkg.add`.
+The package is registered in the `General` package registry and can be installed with:
 
 ```julia
-julia> Pkg.add("Missings")
+julia> using Pkg; Pkg.add("Missings")
 ```
 
 ## Project Status
 
-The package is tested against the current Julia `0.6` release and nightly on Linux, OS X, and Windows.
+Starting from Julia 1.0, the `Missing` type and basic related functionality are part of the language.
+For documentation see [the Julia manual section on missing values](https://docs.julialang.org/en/v1/manual/missing/index.html).
 
-Starting from Julia `0.7` the `Missing` type and basic functionalities related to it have been merged to core Julia.
-This package still provides additional features to handle `missing` values.
+This package provides additional functionality for working with `missing` values:
+- `Missings.nonmissingtype` to extract `T` from a `Union{T, Missing}` type
+- `allowmissing` and `disallowmissing` to convert between `Vector{T}` and `Vector{Union{T, Missing}}`
+- `passmissing` to wrap a function so that it returns `missing` if any of its positional arguments is `missing`
+- `levels` to get the unique values in a vector excluding `missing` and in their preferred order
 
 ## Contributing and Questions
 
-Contributions are very welcome, as are feature requests and suggestions. Please open an
-[issue][issues-url] if you encounter any problems or would just like to ask a question.
-
+Contributions are welcome, as are feature requests and suggestions.
+Please open an [issue][issues-url] if you encounter any problems or would just like to ask a question.
 
 [docs-latest-img]: https://img.shields.io/badge/docs-latest-blue.svg
 [docs-latest-url]: https://JuliaData.github.io/Missings.jl/latest
@@ -45,14 +44,3 @@ Contributions are very welcome, as are feature requests and suggestions. Please
 [codecov-url]: https://codecov.io/gh/JuliaData/Missings.jl
 
 [issues-url]: https://github.com/JuliaData/Missings.jl/issues
-
-[pkg-0.6-img]: http://pkg.julialang.org/badges/Missings_0.6.svg
-[pkg-0.6-url]: http://pkg.julialang.org/?pkg=Missings
-
-## Documentation
-
-Missings.jl provides a single type `Missing` with a single instance `missing` which represents a missing value in data. `missing` values behave essentially like [`NULL` in SQL](https://en.wikipedia.org/wiki/NULL_(SQL)) or [`NA` in R](https://cran.r-project.org/doc/manuals/r-release/R-lang.html#NA-handling). `missing` differs from `nothing` (the object returned by Julia functions and blocks which do not return any value) in that it can be passed to many operators and functions, prompting them to return `missing`. Where appropriate, packages should provide methods propagating `missing` for the functions they define.
-
-The package defines standard operators and functions which propagate `missing` values: for example `1 + missing` and `cos(missing)` both return `missing`. In particular, note that comparison operators `==`, `<`, `>`, `<=` and `=>` (but not `isequal` nor `isless`) also propagate `missing`, so that `1 == missing` and `missing == missing` both return `missing`. Use `ismissing` to test whether a value is `missing`. Logical operators `&`, `|`, `⊻`/`xor` implement [three-valued logic](https://en.wikipedia.org/wiki/Three-valued_logic): they return `missing` only when the result cannot be determined. For example, `true & missing` returns `missing` but `true | missing` returns `true`.
-
-In many cases, `missing` values will have to be skipped or replaced with a valid value. For example, `sum([1, missing])` returns `missing` due to the behavior of `+`. Use `sum(Missings.skip([1, missing])` to ignore `missing` values. `sum(Missings.replace([1, missing], 0))` would have the same effect. `Missings.fail` throws an error if any value is found while iterating over the data. These three functions return an iterator and therefore do not need to allocate a copy of the data. Finally, the `Missings.coalesce` function is a more complex and powerful version of `Missings.replace`.