ffbase (version 0.12.8)

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 ffdfwith assumes that the result must be of the same length as nrow(data). 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

# NOT RUN {
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
# }