The partitions package: enumeration in R

partitions

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Overview

The partitions package provides efficient vectorized code to enumerate solutions to various integer equations. For example, we might note that

5 = 4+1 = 3+2 = 3+1+1 = 2+2+1 = 2+1+1+1 = 1+1+1+1+1

and we might want to list all seven in a consistent format (note here that each sum is written in nonincreasing order, so is considered to be the same as ).

Installation

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

# install.packages("partitions")  # uncomment this to install the package
library("partitions")

The partitions package in use

To enumerate the partitions of 5:

parts(5)
#>                   
#> [1,] 5 4 3 3 2 2 1
#> [2,] 0 1 2 1 2 1 1
#> [3,] 0 0 0 1 1 1 1
#> [4,] 0 0 0 0 0 1 1
#> [5,] 0 0 0 0 0 0 1

(each column is padded with zeros). Of course, larger integers have many more partitions and in this case we can use summary():

summary(parts(16))
#>                                                            
#>  [1,] 16 15 14 14 13 13 13 12 12 12 ... 3 2 2 2 2 2 2 2 2 1
#>  [2,] 0  1  2  1  3  2  1  4  3  2  ... 1 2 2 2 2 2 2 2 1 1
#>  [3,] 0  0  0  1  0  1  1  0  1  2  ... 1 2 2 2 2 2 2 1 1 1
#>  [4,] 0  0  0  0  0  0  1  0  0  0  ... 1 2 2 2 2 2 1 1 1 1
#>  [5,] 0  0  0  0  0  0  0  0  0  0  ... 1 2 2 2 2 1 1 1 1 1
#>  [6,] 0  0  0  0  0  0  0  0  0  0  ... 1 2 2 2 1 1 1 1 1 1
#>  [7,] 0  0  0  0  0  0  0  0  0  0  ... 1 2 2 1 1 1 1 1 1 1
#>  [8,] 0  0  0  0  0  0  0  0  0  0  ... 1 2 1 1 1 1 1 1 1 1
#>  [9,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 1 1 1 1 1 1 1 1
#> [10,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 0 1 1 1 1 1 1 1
#> [11,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 0 0 1 1 1 1 1 1
#> [12,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 0 0 0 1 1 1 1 1
#> [13,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 0 0 0 0 1 1 1 1
#> [14,] 0  0  0  0  0  0  0  0  0  0  ... 1 0 0 0 0 0 0 1 1 1
#> [15,] 0  0  0  0  0  0  0  0  0  0  ... 0 0 0 0 0 0 0 0 1 1
#> [16,] 0  0  0  0  0  0  0  0  0  0  ... 0 0 0 0 0 0 0 0 0 1

Sometimes we want to find the unequal partitions (that is, partitions without repeats):

summary(diffparts(16))
#>                                                           
#> [1,] 16 15 14 13 13 12 12 11 11 11 ... 8 8 7 7 7 7 7 6 6 6
#> [2,] 0  1  2  3  2  4  3  5  4  3  ... 5 4 6 6 5 5 4 5 5 4
#> [3,] 0  0  0  0  1  0  1  0  1  2  ... 2 3 3 2 4 3 3 4 3 3
#> [4,] 0  0  0  0  0  0  0  0  0  0  ... 1 1 0 1 0 1 2 1 2 2
#> [5,] 0  0  0  0  0  0  0  0  0  0  ... 0 0 0 0 0 0 0 0 0 1

Restricted partitions

Sometimes we have restrictions on the partition. For example, to enumerate the partitions of 9 into 5 parts we would use restrictedparts():

summary(restrictedparts(9,5))
#>                                                 
#> [1,] 9 8 7 6 5 7 6 5 4 5 ... 5 4 4 3 3 5 4 3 3 2
#> [2,] 0 1 2 3 4 1 2 3 4 2 ... 2 3 2 3 2 1 2 3 2 2
#> [3,] 0 0 0 0 0 1 1 1 1 2 ... 1 1 2 2 2 1 1 1 2 2
#> [4,] 0 0 0 0 0 0 0 0 0 0 ... 1 1 1 1 2 1 1 1 1 2
#> [5,] 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 1 1 1 1 1

and if we want the partitions of 9 into parts not exceeding 5 we would use the conjugate of this:

summary(conjugate(restrictedparts(9,5)))
#>                                                  
#>  [1,] 1 2 2 2 2 3 3 3 3 3 ... 4 4 4 4 4 5 5 5 5 5
#>  [2,] 1 1 2 2 2 1 2 2 2 3 ... 2 2 3 3 4 1 2 2 3 4
#>  [3,] 1 1 1 2 2 1 1 2 2 1 ... 1 2 1 2 1 1 1 2 1 0
#>  [4,] 1 1 1 1 2 1 1 1 2 1 ... 1 1 1 0 0 1 1 0 0 0
#>  [5,] 1 1 1 1 1 1 1 1 0 1 ... 1 0 0 0 0 1 0 0 0 0
#>  [6,] 1 1 1 1 0 1 1 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
#>  [7,] 1 1 1 0 0 1 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
#>  [8,] 1 1 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
#>  [9,] 1 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0

Block parts

Sometimes we have restrictions on each element of a partition and in this case we would use blockparts():

summary(blockparts(1:6,10))
#>                                                 
#> [1,] 1 1 1 1 0 1 1 1 0 1 ... 0 1 0 0 0 1 0 0 0 0
#> [2,] 2 2 2 1 2 2 2 1 2 2 ... 0 0 1 0 0 0 1 0 0 0
#> [3,] 3 3 2 3 3 3 2 3 3 1 ... 2 0 0 1 0 0 0 1 0 0
#> [4,] 4 3 4 4 4 2 3 3 3 4 ... 0 1 1 1 2 0 0 0 1 0
#> [5,] 0 1 1 1 1 2 2 2 2 2 ... 2 2 2 2 2 3 3 3 3 4
#> [6,] 0 0 0 0 0 0 0 0 0 0 ... 6 6 6 6 6 6 6 6 6 6

which would show all solutions to \sum_{i=1}^6a_i=9, .

Compositions

Above we considered and to be the same partition, but if these are considered to be distinct, we need the compositions, not partitions:

compositions(4)
#>                     
#> [1,] 4 1 2 1 3 1 2 1
#> [2,] 0 3 2 1 1 2 1 1
#> [3,] 0 0 0 2 0 1 1 1
#> [4,] 0 0 0 0 0 0 0 1

Set partitions

A set of 4 elements, WLOG \{1,2,3,4\}, may be partitioned into subsets in a number of ways and these are enumerated with the setparts() function:

setparts(4)
#>                                   
#> [1,] 1 1 1 1 2 1 1 1 1 1 1 2 2 2 1
#> [2,] 1 1 1 2 1 2 1 2 2 1 2 1 1 3 2
#> [3,] 1 2 1 1 1 2 2 1 3 2 1 3 1 1 3
#> [4,] 1 1 2 1 1 1 2 2 1 3 3 1 3 1 4

In the above, column 2 3 1 1 would correspond to the set partition \{\{3,4\},\{1\},\{2\}\}.

Multiset

Knuth deals with multisets (that is, a generalization of the concept of set, in which elements may appear more than once) and gives an algorithm for enumerating a multiset. His simplest example is the permutations of \{1,2,2,3\}:

multiset(c(1,2,2,3))
#>                             
#> [1,] 1 1 1 2 2 2 2 2 2 3 3 3
#> [2,] 2 2 3 1 1 2 2 3 3 1 2 2
#> [3,] 2 3 2 2 3 1 3 1 2 2 1 2
#> [4,] 3 2 2 3 2 3 1 2 1 2 2 1

It is possible to answer questions such as the permutations of the word “pepper”:

library("magrittr")

"pepper"    %>%
strsplit("") %>%
unlist        %>%
match(letters) %>%
multiset        %>%
apply(2,function(x){x %>% `[`(letters,.) %>% paste(collapse="")})
#>  [1] "eepppr" "eepprp" "eeprpp" "eerppp" "epeppr" "epeprp" "eperpp" "eppepr"
#>  [9] "epperp" "eppper" "epppre" "epprep" "epprpe" "eprepp" "eprpep" "eprppe"
#> [17] "ereppp" "erpepp" "erppep" "erpppe" "peeppr" "peeprp" "peerpp" "pepepr"
#> [25] "peperp" "pepper" "peppre" "peprep" "peprpe" "perepp" "perpep" "perppe"
#> [33] "ppeepr" "ppeerp" "ppeper" "ppepre" "pperep" "pperpe" "pppeer" "pppere"
#> [41] "pppree" "ppreep" "pprepe" "pprpee" "preepp" "prepep" "preppe" "prpeep"
#> [49] "prpepe" "prppee" "reeppp" "repepp" "reppep" "repppe" "rpeepp" "rpepep"
#> [57] "rpeppe" "rppeep" "rppepe" "rpppee"

Further information

For more detail, see the package vignettes

vignette("partitionspaper")
vignette("setpartitions")
vignette("scrabble")