类似于R的枚举式论证 [英] Enum-like arguments in R
问题描述
EnumTest = function(enum = c(BLUE RED,BLACK)){
enumArg < -
switch(
match.arg(enum),BLUE= 0L,RED= 1L,BLACK= 2L
)
switch(enumArg,
#do something
)
}
是否有更好/更简洁的方式来模仿R中的类似枚举的行为?例如。一个大的问题,用户必须知道参数的一组可能的值,并手动键入它作为一个字符串 - 没有任何建议或自动完成...
如果没有其他更好的方法,有一件事情可以改进上述方法 - 通过在全球范围内预先定义枚举或者说R6类的私人成员来说,这样做可以更简洁:
颜色< - c(BLUE,RED,BLACK)
然后可以(重新)在一个或多个函数定义中使用它,例如:
EnumTest = function(enum = Color){
...
m不知道如何在 match.arg
函数中使用这个颜色
矢量。如果我可以将颜色
定义为一个地图,那么实际的颜色值和值就是整数表示,那么这是很好的 - 但我不知道这是多么明智。无论如何,也许存在更常见的整齐方法。
主要目标是为我的包和功能的用户提供一个易于使用的直观界面(例如,轻松找到可能的值集,tab-completion,自动建议等),然后使用枚举类的参数来定义这些函数的开发
如何使用定义枚举的函数返回 list(a =a,...)
?然后,您可以将返回的向量分配给变量,并在上下文中使用它,或直接使用该函数。名称或整数引用将作为索引使用,尽管您必须使用索引查找的未列出版本 [[
,否则您将获得一个包含一个元素的列表。
colorEnum< - function(){
list(BLUE =BLUE,RED =RED ,BLACK =BLACK)
}
colorEnum()$ BLUE
#> [1]BLUE
colorEnum()[[1]]
#> [1]BLUE
colorEnum()[1]
#> $ BLUE
#> [1]BLUE
col< - colorEnum()
col $ BLUE
#> [1]BLUE
col [[1]]
#> [1]BLUE
col $ BAD_COLOR
#> NULL
col [[5]]
#> col [[5]]中的错误:下标超出限制
您可以获取名称列表在一个匹配中使用,即你的函数参数可以是
EnumTest = function(enum = names(colorEnum()){..
你也可以缩写,但它必须是唯一的(如果使用RStudio, code> col 是一个列表,它会建议完成!)
col $ BLA
#> [1]BLACK
col $ BL
#> NULL
如果你想要更复杂的枚举处理,你可以将S3类分配给你的枚举构造函数返回的东西,并在类enum上写一个小的函数集,并允许不区分大小写的索引。您还可以添加特殊功能来处理特定的类,例如colorEnum;我没有这样做。继承意味着列表访问方法仍然可以工作。
colorEnum2< - functio n(){
结构(
list(BLUE =BLUE,RED =RED,BLACK =BLACK),
class = c(colorEnum2 ,list)
)
}
#注意,更改示例允许多个返回值。
`[.enum`< - function(x,i){
if(is.character(i))
i< - toupper(i)
class )< - list
names(as.list(x)[i])
}
`[[.enum`< - function(x,i ,exact = FALSE){
if(is.character(i))
i < - toupper(i)
class(x)< - list
as。列表(x)[[i,exact = exact]]
}
`$ .enum`< - function(x,name){
x [[name]
}
col< - colorEnum2()
#所有这些返回[1]RED
col $ red
col $ r
col [[red]]
col [[r]]
col [red]
col [c(red,BLUE )]
#> [1]REDBLUE
col [r]
[1] NA#R不匹配部分字符串与[
这些覆盖内置的 [
, [[ / code>和
$
函数,当索引的东西是类枚举,对于任何枚举类对象。如果你需要另外一个,你只需要定义它。
directionEnum< - function(){
结构(
列表(LEFT =LEFT RIGHT =RIGHT),
class = c(directionEnum,enum,list)
)
}
directionEnum()$ l
#> [1]LEFT
如果您需要几个枚举对象,可以添加工厂函数枚举
,它需要一个字符串和名称的向量,并返回一个枚举
对象。大部分只是验证。
枚举< - function(enums,name = NULL){
if长度(枚举)< 1)
stop(枚举可能不为空)
枚举< - toupper(as.character(enums))
uniqueEnums< - unique枚举)
如果(!same(enums,uniqueEnums))
stop(枚举必须是唯一的(忽略大小写))
validNames< - make.names(enums)
if(!identical(enums,validNames))
stop(枚举必须是有效的R标识符)
enumClass< - c(name,枚举,列表)
obj< - as.list(枚举)
名称(obj)< - 枚举
结构(obj,class = enumClass)
}
col< - enum(c(BLUE,red,Black),name =TheColors)
col $ R
#> [1]RED
class(col)
#> [1]TheColorsenumlist
side< - enum(c(left,right))
side $ L
#> ; [1]LEFT
class(side)
#> [1]枚举列表
但是现在开始看起来像一个包.. 。
I'm new to R and I'm currently trying to supply the enumeration-like argument to the R function (or the RC/R6 class method), I currently use character vector plus match.arg
similar to the following:
EnumTest = function(enum = c("BLUE", "RED", "BLACK")) {
enumArg <-
switch(
match.arg(enum), "BLUE" = 0L, "RED" = 1L, "BLACK" = 2L
)
switch(enumArg,
# do something
)
}
Is there are better/more concise way to imitate enum-like behavior in R? E.g. one big problem that user has to know the set of possible values for the argument and manually type it as a string - without any suggestion or auto-completion...
If there is no other better way, one thing that could improve above approach - it'd be nice to make it more concise by say predefining enums globally or say as private members of R6 class:
Color <- c("BLUE", "RED", "BLACK")
Then one could (re)use it in one or more function definitions, e.g.:
EnumTest = function(enum = Color) {
...
However, I'm not sure how to use this Color
vector in match.arg
function. It'd be nice if I could define Color
as a map with keys being actual color values and values being integer representation - but I'm not sure how sensible that is.. Anyways, maybe there are more common neat approaches exist.
The main goal would be to provide an easy-to-use intuitive interface to the user of my package and functions (e.g. easy way to find the set of possible values, tab-completion, auto-suggestion, etc..), followed by standardized development of such functions using enum-like arguments
How about using a function that defines the enum by returning list(a= "a", ...)
? You can then either assign the returned vector to a variable and use it in context, or use the function directly. Either a name or an integer reference will work as an index, although you have to use the unlist version of the index lookup, [[
, otherwise you get a list with one element.
colorEnum <- function() {
list(BLUE = "BLUE", RED = "RED", BLACK = "BLACK")
}
colorEnum()$BLUE
#> [1] "BLUE"
colorEnum()[[1]]
#> [1] "BLUE"
colorEnum()[1]
#> $BLUE
#> [1] "BLUE"
col <- colorEnum()
col$BLUE
#> [1] "BLUE"
col[[1]]
#> [1] "BLUE"
col$BAD_COLOR
#> NULL
col[[5]]
#> Error in col[[5]] : subscript out of bounds
You can get the list of names for use in a match, i.e. your function parameter could be
EnumTest = function( enum = names(colorEnum()) { ...
You can actually abbreviate too, but it must be unique. (If you use RStudio, since col
is a list, it will suggest completions!)
col$BLA
#> [1] "BLACK"
col$BL
#> NULL
If you want more sophisticated enum handling, you could assign S3 classes to the thing returned by your enum constructor function and write a small collection of functions to dispatch on class "enum" and allow case-insensitive indexing. You could also add special functions to work with a specific class, e.g. "colorEnum"; I have not done that here. Inheritance means the list access methods all still work.
colorEnum2 <- function() {
structure(
list(BLUE = "BLUE", RED = "RED", BLACK = "BLACK"),
class= c("colorEnum2", "enum", "list")
)
}
# Note, changed example to allow multiple returned values.
`[.enum` <- function(x, i) {
if ( is.character( i ))
i <- toupper(i)
class(x) <- "list"
names(as.list(x)[i])
}
`[[.enum` <- function(x, i, exact= FALSE) {
if ( is.character( i ))
i <- toupper(i)
class(x) <- "list"
as.list(x)[[i, exact=exact]]
}
`$.enum` <- function(x, name) {
x[[name]]
}
col <- colorEnum2()
# All these return [1] "RED"
col$red
col$r
col[["red"]]
col[["r"]]
col["red"]
col[c("red", "BLUE")]
#> [1] "RED" "BLUE"
col["r"]
[1] NA # R does not matches partial strings with "["
These override the built in [
, [[
and $
functions when the thing being indexed is of class "enum", for any "enum" classed objects. If you need another one, you just need to define it.
directionEnum <- function() {
structure(
list(LEFT = "LEFT", RIGHT = "RIGHT"),
class= c("directionEnum", "enum", "list")
)
}
directionEnum()$l
#> [1] "LEFT"
If you need several enum objects, you could add a factory function enum
that takes a vector of strings and a name and returns an enum
object. Most of this is just validation.
enum <- function(enums, name= NULL) {
if (length(enums) < 1)
stop ("Enums may not be empty." )
enums <- toupper(as.character(enums))
uniqueEnums <- unique(enums)
if ( ! identical( enums, uniqueEnums ))
stop ("Enums must be unique (ignoring case)." )
validNames <- make.names(enums)
if ( ! identical( enums, validNames ))
stop( "Enums must be valid R identifiers." )
enumClass <- c(name, "enum", "list")
obj <- as.list(enums)
names(obj) <- enums
structure( obj, class= enumClass)
}
col <- enum(c("BLUE", "red", "Black"), name = "TheColors")
col$R
#> [1] "RED"
class(col)
#> [1] "TheColors" "enum" "list"
side <- enum(c("left", "right"))
side$L
#> [1] "LEFT"
class(side)
#> [1] "enum" "list"
But now this is starting to look like a package...
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