Path-Based Access and Manipulation of Nested Lists • slash

The goal of slash is to provide a hierarchical key-value store where elements can be accessed and modified using simple path-like strings, such as "cars/1/model" or "garage/vw/golf/color".

It supports:

Named and unnamed lists
Nested access with / paths
Optional strict mode
List path enumeration
Full get/set/delete API

Installation

You can install slash from CRAN with:

install.packages("slash")

You can install the development version of slash like so:

devtools::install_github("feddelegrand7/slash")

Getting elements from a `list`

Consider the following list object:

cars_list <- list(
  cars = list(
    list(manufacturer = "VW", model = "Golf V", year = 2005),
    list(manufacturer = "Toyota", model = "Corolla", year = 2010),
    list(manufacturer = "Tesla", model = "Model S", year = 2022)
  )
)

If one wants to access the manufacturer element, one can do:

cars_list$cars[[1]]$manufacturer
#> [1] "VW"

Using slash, you can access the same element using a file-path syntax:

library(slash)

sl <- slash$new(data = cars_list)

sl$get(path = "cars/1/manufacturer")
#> [1] "VW"

slash can operate on unnamed elements like above and/or on named elements like the following:

garage <- list(
  vw = list(
    golf = list(year = 2005, color = "black"),
    passat = list(year = 2011)
  ),
  toyota = list(
    corolla = list(year = 2010)
  )
)

Let’s say we want to access the color of the VW Golf. While in standard R one can do:

garage$vw$golf$color
#> [1] "black"

Using slash, we can operate as the following:

sl <- slash$new(data = garage)
sl$get("vw/golf/color")
#> [1] "black"

If now, for example, we would want to access all the properties of the Golf car, we would do:

sl <- slash$new(data = garage)
sl$get("vw/golf")
#> $year
#> [1] 2005
#> 
#> $color
#> [1] "black"

It is possible to return the whole list if needed using the get_all method:

sl$get_all()
#> $vw
#> $vw$golf
#> $vw$golf$year
#> [1] 2005
#> 
#> $vw$golf$color
#> [1] "black"
#> 
#> 
#> $vw$passat
#> $vw$passat$year
#> [1] 2011
#> 
#> 
#> 
#> $toyota
#> $toyota$corolla
#> $toyota$corolla$year
#> [1] 2010

You’ll also get the whole list element when NULL (the default) is provided to the get method:

sl$get(NULL)
#> $vw
#> $vw$golf
#> $vw$golf$year
#> [1] 2005
#> 
#> $vw$golf$color
#> [1] "black"
#> 
#> 
#> $vw$passat
#> $vw$passat$year
#> [1] 2011
#> 
#> 
#> 
#> $toyota
#> $toyota$corolla
#> $toyota$corolla$year
#> [1] 2010

If you try to access an element that does not exist, you’ll get a NULL as the returned value:

sl$get("vw/polo")
#> NULL

You can change this behavior and get an error back when an element is not found using the strict parameter. You can set the parameter at the initialization of the instance:

sl <- slash$new(data = garage, strict = TRUE)

or afterward, using the set_strict method:

sl$set_strict(strict = TRUE)

This way, we get an error back when an element is not found:

sl$get("vw/polo")
#> Error in sl$get("vw/polo"): Element at path 'vw/polo' does not exist

Setting elements in a `list`

You can change the value of an element or add a new element within a list using the set method, suppose I want to add a new car to my previous list:

sl$set(path = "vw/polo/year", value = 2013)
sl$set(path = "vw/polo/color", value = "Steelblue")

sl$get("vw")
#> $golf
#> $golf$year
#> [1] 2005
#> 
#> $golf$color
#> [1] "black"
#> 
#> 
#> $passat
#> $passat$year
#> [1] 2011
#> 
#> 
#> $polo
#> $polo$year
#> [1] 2013
#> 
#> $polo$color
#> [1] "Steelblue"

Now, if you want to modify the year from 2013 to 2023 for example, you can do:

sl$set(path = "vw/polo/year", value = 2023)
sl$get("vw")
#> $golf
#> $golf$year
#> [1] 2005
#> 
#> $golf$color
#> [1] "black"
#> 
#> 
#> $passat
#> $passat$year
#> [1] 2011
#> 
#> 
#> $polo
#> $polo$year
#> [1] 2023
#> 
#> $polo$color
#> [1] "Steelblue"

You can even build your list element from scrath:

sl <- slash$new()
sl$get()
#> list()

sl$set("vw/golf/year", value = 2005)
sl$set("vw/golf/color", value = "black")
sl$set("vw/passat/year", value = 2011)
sl$set("vw/polo/year", value = "Steelblue")
sl$set("vw/polo/color", value = 2023)

sl$get("vw")
#> $golf
#> $golf$year
#> [1] 2005
#> 
#> $golf$color
#> [1] "black"
#> 
#> 
#> $passat
#> $passat$year
#> [1] 2011
#> 
#> 
#> $polo
#> $polo$year
#> [1] "Steelblue"
#> 
#> $polo$color
#> [1] 2023

Deleting an element from the `list`

You can delete an element using the delete method, suppose we don’t need the polo car element anymore, we could do:

sl$delete("vw/polo")
sl$get("vw")
#> $golf
#> $golf$year
#> [1] 2005
#> 
#> $golf$color
#> [1] "black"
#> 
#> 
#> $passat
#> $passat$year
#> [1] 2011

You can delete at any level on the list, for example if we want to delete the color field of the golf element, we could do:

sl$delete("vw/golf/color")
sl$get("vw")
#> $golf
#> $golf$year
#> [1] 2005
#> 
#> 
#> $passat
#> $passat$year
#> [1] 2011

Listing the available paths

If you want to list the available paths of your list object, you can call the list_paths() method:

sl$list_paths()
#> [1] "vw"             "vw/golf"        "vw/golf/year"   "vw/passat"     
#> [5] "vw/passat/year"

Check if an element exists:

Use the exists method to check if a particular path exists:

sl$exists("vw")
#> [1] TRUE
sl$exists("vw/golf")
#> [1] TRUE
sl$exists("vw/golf/color")
#> [1] FALSE
sl$exists("porshe/911")
#> [1] FALSE

Printing a `slash` object

A slash object has a particular print method attached to it, it prints a nice view of the available paths among other information (strict mode):

sl
#> slash object (non-strict mode)
#> Use $get() or $get_all() to view contents
#> Available Paths:
#> - vw
#> - vw/golf
#> - vw/golf/year
#> - vw/passat
#> - vw/passat/year

Printing the `list` object

Each slash object is build on top of a list object, if you want to print the list it-self, use the print_list method:

sl$print_list()
#> list(vw = list(golf = list(year = 2005), passat = list(year = 2011)))

Printing a `Tree` representation

only available in the development version (not yet on CRAN)

You can print a Tree representation of your slash object and its underlying list using the print_tree method:

sl$print_tree()
#> <root> 
#> └── vw
#>     ├── golf
#>     │   └── year: 2005
#>     └── passat
#>         └── year: 2011

# Adding the 208 peugeot model
# Make sure to quote the `208`, otherwise slash will 
# understand it as indices (Not name)

sl$set("peugeot/`208`/year", 2013)

sl$print_tree()
#> <root> 
#> ├── vw
#> │   ├── golf
#> │   │   └── year: 2005
#> │   └── passat
#> │       └── year: 2011
#> └── peugeot
#>     └── `208`
#>         └── year: 2013

sl$print_tree("peugeot")
#> peugeot 
#> └── `208`
#>     └── year: 2013

sl$set("peugeot/`208`/energy/class", "Diesel")
sl$print_tree("peugeot/`208`/energy")
#> peugeot/`208`/energy 
#> └── class: Diesel

Code of Conduct

Please note that the slash project is released with a Contributor Code of Conduct. By contributing to this project, you agree to abide by its terms.

slash

Installation

Getting elements from a list

Setting elements in a list

Deleting an element from the list