ffbase (version 0.6-2)

ffdfwith: Evaluate an expression in a ffdf data environment

Description

Evaluate an R expression in an environment constructed from a ffdata data frame. Faster than with.ffdf, but in constrast ffdfwith can change the original data. Please note that you should write your expression as if it is a normal data.frame. The resulting return value however will be a ffdf object.

Usage

ffdfwith(data, expr, ...)

Arguments

data

ffdf data object used as an environment for evaluation.

expr

expression to evaluate.

...

arguments to be passed to future methods.

Value

• if expression is a vector a newly created ff vector will be returned otherwise if the expression is a data.frame a newly created ffdf object will be returned.

Examples

dat <- data.frame(x=1:10, y=10:1)
ffdat <- as.ffdf(dat)

ffdfwith(ffdat, {
   x <- x + 1
   x + y
})

#notice that x has been altered
ffdat$x