itemMatrix-class {arules}R Documentation

Class “itemMatrix” - Sparse Binary Matrix to Represent Sets of Items

Description

The itemMatrix class is the basic building block for transactions, itemsets and rules in package arules. The class contains a sparse Matrix representation of items (a set of itemsets or transactions) and the corresponding item labels.

Objects from the Class

Objects can be created by calls of the form new("itemMatrix", ...). However, most of the time objects will be created by coercion from a matrix, list or data.frame.

Slots

data:
Object of class dgCMatrix which stores item occurrences in sparse representation. Note that the dgCMatrix is column-oriented and itemMatrix is row-oriented with each row representing an element (an itemset, a transaction, etc.). As a result, the dgCMatrix in this slot is always a transposed version of the binary incidence matrix in itemMatrix.
itemInfo:
Object of class "data.frame" which contains named vectors of the length equal to the number of elements in the set. If the slot is not empty (contains no item labels), the first element in the data.frame must have the name "labels" and contain a character vector with the item labels used for representing an item. In addition to the item labels, the data.frame can contain arbitrary named vectors (of the same length) to represent, e.g., variable names and values which were used to create the binary items or hierarchical category information associated with each item label. This information is used for the %in% method in this class. The subset method in associations can use this method to select subsets of associations containing items with matching variable or category names.

Methods

[
signature(x = "itemMatrix"); extracts parts of the itemMatrix. The first argument selects rows (e.g., transactions or rules) and the second argument selects columns (items). Either argument can be omitted to select all rows or columns.
coerce
signature(from = "matrix", to = "itemMatrix")
coerce
signature(from = "list", to = "itemMatrix")
coerce
signature(from = "itemMatrix", to = "dgCMatrix")
; access the sparse matrix representation. Note, the dgCMatrix contains a transposed from of the itemMatrix.
coerce
signature(from = "itemMatrix", to = "matrix")
coerce
signature(from = "itemMatrix", to = "list")
decode
signature(x = "itemMatrix"); decodes the numeric items codes (column numbers in the itemMatrix) given in argument items to the item names using the labels stored in x. items can be a vector or list.
dim
signature(x = "itemMatrix"); returns the dimensions of the itemMatrix.
image
signature(x = "itemMatrix"); plots an image of the itemMatrix for visual inspection.
%in%
signature(x = "itemMatrix"): matches values against the item labels (and the additional information) for each element (row) in the itemMatrix.
itemLabels
signature(object = "itemMatrix"); returns the item labels as a character vector.
itemLabels<-
signature(object = "itemMatrix"); replaces the item labels.
itemInfo
signature(object = "itemMatrix"); returns the whole item information data.frame including labels.
itemInfo<-
signature(object = "itemMatrix"); replaces the item info by a data.frame. The length of the vectors in the data.frame has to match the number of elements (rows) in the itemMatrix.
labels
signature(x = "transactions"); returns the labels (item labels and element names) for the matrix as a list of two vectors named items and elements.
length
signature(x = "itemMatrix"); returns the number of elements (rows) in the itemMatrix.
show
signature(object = "itemMatrix")
summary
signature(object = "itemMatrix")

Author(s)

Michael Hahsler

See Also

transactions-class, itemsets-class, rules-class

Examples

## Generate random data and coerce data to itemMatrix.
m <- matrix(as.integer(runif(100000)>0.8), ncol=20)
dimnames(m) <- list(NULL, paste("item", c(1:20), sep=""))
i <- as(m, "itemMatrix")

## Get the number of elements (rows) in the itemMatrix.
length(i)

## Get first 5 elements (rows) of the itemMatrix as list.
as(i[1:5], "list")

[Package arules version 0.1-1 Index]