R: Evaluate an expression in a ffdf data environment

ffdfwith {ffbase} | R Documentation

## 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

    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

[Package ffbase version 0.13.1 Index]