Creates a unique integer key for unique combinations of rows of an ffdf

Description

Creates a unique integer key for unique combinations of rows of an ffdf. In database terms this would correspond to a primary or foreign key.
Orders the ffdf decreasingly alongside the columns with NA's as last in the order and creates the integer key.

Usage

ikey(x, ...)

Arguments

Value

An integer ff vector of the same length as the number of rows in x with unique values for each unique row

Examples

oldffmaxbytes <- getOption("ffmaxbytes")
options(ffmaxbytes = 20)
ffiris <- as.ffdf(iris)
ffiris$key1 <- ikey(ffiris)
ffiris$key2 <- ikey(ffiris[c("Petal.Width","Species")])
unique(ffiris[c("key2","Petal.Width","Species")])[,]
options(ffmaxbytes = oldffmaxbytes)