CODEWITHSUNDEEP
r
Dave
Dave

Reputation: 2386

Creating a similar function to "." from Plyr

Hoping that someone could post an example of a custom function which acts similar to "." in plyr.

What I have is a data frame. Where I am continuously running queries such as:

sqldf("select * from event.df where Date in (select Date from condition.df where C_1 = 1 and (C_2 = 1 OR C_3 = 3)")

What I would like is to have a function which basically acts as follows:

.(C_1, C_2 + C_3)

Specifically, a vector of formulas which define the attributes I use to select my data. I can treat "+" as OR "*" as AND etc...

I tried looking at the return type for "." from plyr but did not understand it.

Upvotes: 0

Views: 146

Answers (2)

Dave
Dave

Reputation: 2386

parse <- function (formula, blank.char = ".") 
{
    formula <- paste(names(formula), collapse = "")
    vars <- function(x) {
        if (is.na(x)) 
            return(NULL)
        remove.blank(strsplit(gsub("\\s+", "", x), "[*+]")[[1]])
    }
    remove.blank <- function(x) {
        x <- x[x != blank.char]
        if (length(x) == 0) 
            NULL
        else x
    }
    parts <- strsplit(formula, "\\|")[[1]]
    list(m = lapply(strsplit(parts[1], "~")[[1]], vars), l = lapply(strsplit(parts[2],  "~")[[1]], vars))
}

parse(.(a + b ~ c + d | e))

    $m
$m[[1]]
[1] "a" "b"

$m[[2]]
[1] "c" "d"


$l
$l[[1]]
[1] "e"

Upvotes: 0

Andrie
Andrie

Reputation: 179448

A function similar to plyr:::. is plyr:::.:

plyr:::.
function (..., .env = parent.frame()) 
{
    structure(as.list(match.call()[-1]), env = .env, class = "quoted")
}
<environment: namespace:plyr>

This returns a list and assigns it a class "quoted". All it does, is to match the arguments of .() to the column names in the enclosing environment. Try it in a different context:

with(iris, .(Sepal.Length, Species))
List of 2
 $ Sepal.Length: symbol Sepal.Length
 $ Species     : symbol Species
 - attr(*, "env")=<environment: 0x2b33598> 
 - attr(*, "class")= chr "quoted"

What you do with this object next, depends on your purpose. Several methods exist for working with this class:

methods(class="quoted")
[1] as.quoted.quoted* c.quoted*         names.quoted*     print.quoted*     [.quoted*        

   Non-visible functions are asterisked

So, if you're looking for a function like .(), perhaps you can simply use .()

Upvotes: 6

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