Perform Recursive Computations

Mass rollup for a Bill of Materials is an example of a class of computations in which elements are arranged in a tree structure and some property of each element is a computed function of the corresponding values of its child elements. Leaf elements, i.e., those with no children, have values assigned. In many cases, the combining function is simple arithmetic sum; in other cases (e.g., mass properties), the combiner may involve other information such as the geometric relationship between parent and child, or statistical relations such as root-sum-of-squares (RSS). This package implements a general function for such problems. It is adapted to specific recursive computations by functional programming techniques; the caller passes a function as the update parameter to rollup() (or, at a lower level, passes functions as the get, set, combine, and override parameters to update_prop()) at runtime to specify the desired operations. The implementation relies on graph-theoretic algorithms from the 'igraph' package of Csárdi, et al. (2006 ).

rollupTree

rollupTree implements a general function for computations in which some property of a parent element is a combination of corresponding properties of its child elements. The mass of an assembly, for example, is the sum of the masses of its subassemblies, and the mass of each subassembly is the sum of masses of its parts, etc.

rollupTree can perform computations specified by arbitrarily-shaped (but well-formed) trees, arbitrarily-defined properties and property-combining operations. Defaults are provided to simplify common cases (atomic numerical properties combined by summing), but functional programming techniques allow the caller to pass arbitrary update methods as required.

Despite its name, rollupTree can operate on directed acyclic graphs that are not trees if instructed to apply less stringent validation rules to its input.

Installation

install.packages("rollupTree")

You can install the development version of rollupTree from GitHub with:

# install.packages("pak")
pak::pak("jsjuni/rollupTree")

Example

Suppose we have this data frame representing a work breakdown structure:

library(rollupTree)
wbs_table
#>     id  pid                    name budget
#> 1  top <NA> Construction of a House     NA
#> 2    1  top                Internal     NA
#> 3    2  top              Foundation     NA
#> 4    3  top                External     NA
#> 5  1.1    1              Electrical  25000
#> 6  1.2    1                Plumbing  61000
#> 7  2.1    2                Excavate  37000
#> 8  2.2    2          Steel Erection   9000
#> 9  3.1    3            Masonry Work  62000
#> 10 3.2    3       Building Finishes  21500

and this tree with edges representing child-parent relations in the breakdown:

igraph::E(wbs_tree)
#> + 9/9 edges from dd17ef5 (vertex names):
#> [1] 1  ->top 2  ->top 3  ->top 1.1->1   1.2->1   2.1->2   2.2->2   3.1->3  
#> [9] 3.2->3

We can sum the budget numbers as follows:

rollup(
  tree=wbs_tree,
  ds=wbs_table,
  update=function(d, t, s) update_df_prop_by_id(df=d, target=t, sources=s, prop="budget"),
  validate_ds=function(t, d) validate_df_by_id(tree=t, df=d, prop="budget")
)
#>     id  pid                    name budget
#> 1  top <NA> Construction of a House 215500
#> 2    1  top                Internal  86000
#> 3    2  top              Foundation  46000
#> 4    3  top                External  83500
#> 5  1.1    1              Electrical  25000
#> 6  1.2    1                Plumbing  61000
#> 7  2.1    2                Excavate  37000
#> 8  2.2    2          Steel Erection   9000
#> 9  3.1    3            Masonry Work  62000
#> 10 3.2    3       Building Finishes  21500