deflist

The goal of deflist is to provide a list-like object for which element access is routed through a user-supplied function. This can be used, for example, when list-like syntax is required but one cannot afford to hold all elements in memory at once.

Installation

You can install the released version of deflist from CRAN with:

install.packages("deflist")

And the development version from GitHub with:

# install.packages("remotes")
remotes::install_github("bbuchsbaum/deflist")

Examples

library(deflist)

dl <- deflist(function(i) i, len=10)
print(dl[[1]])
#> [1] 1

calls <- integer()
dl2 <- deflist(function(i) {
  calls <<- c(calls, i)
  i * 2
}, len = 10)
print(dl2[[1]])
#> [1] 2
print(dl2[[3]])
#> [1] 6
print(calls)
#> [1] 1 3

The value at an index may change across calls, for example:

set.seed(1)
dl3 <- deflist(function(i) { rnorm(1) }, len=10)
print(dl3[[1]])
#> [1] -0.6264538
print(dl3[[1]])
#> [1] 0.1836433

Memoisation can be enabled so that values at a given index are cached:

set.seed(1)
dl4 <- deflist(function(i) { rnorm(1)  }, len=10, memoise=TRUE)
print(dl4[[1]])
#> [1] -0.6264538
print(dl4[[1]])
#> [1] -0.6264538

In addition, memoisation can be set to store cached values to the file system:

set.seed(1)
dl5 <- deflist(function(i) { rnorm(1000)  }, len=10, memoise=TRUE, cache="file", cachedir = tempdir())
print(dl5[[1]][1:10])
#>  [1] -0.6264538  0.1836433 -0.8356286  1.5952808  0.3295078 -0.8204684
#>  [7]  0.4874291  0.7383247  0.5757814 -0.3053884
print(dl5[[1]][1:10])
#>  [1] -0.6264538  0.1836433 -0.8356286  1.5952808  0.3295078 -0.8204684
#>  [7]  0.4874291  0.7383247  0.5757814 -0.3053884