itemMatrix-class           package:arules           R Documentation

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_o_f _I_t_e_m_s

_D_e_s_c_r_i_p_t_i_o_n:

     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.

_O_b_j_e_c_t_s _f_r_o_m _t_h_e _C_l_a_s_s:

     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'.

_S_l_o_t_s:

     '_d_a_t_a': 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'.

     '_i_t_e_m_I_n_f_o': 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.

_M_e_t_h_o_d_s:

     [ '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.

     _c_o_e_r_c_e 'signature(from = "matrix", to = "itemMatrix")'

     _c_o_e_r_c_e 'signature(from = "list", to = "itemMatrix")'

     _c_o_e_r_c_e 'signature(from = "itemMatrix", to = "matrix")'

     _c_o_e_r_c_e 'signature(from = "itemMatrix", to = "list")'

     _d_e_c_o_d_e '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.

     _d_i_m 'signature(x = "itemMatrix")'; returns the dimensions of the
          itemMatrix.

     _i_m_a_g_e 'signature(x = "itemMatrix")'; plots an image of the
          itemMatrix for visual inspection.

     %_i_n% 'signature(x = "itemMatrix")': matches values  against the
          item labels (and the additional information) for  each
          element (row) in the itemMatrix.

     _l_a_b_e_l_s 'signature(object = "itemMatrix")'; returns the item labels
          as a 'character' vector.

     _l_a_b_e_l_s<- 'signature(object = "itemMatrix")'; replaces the item
          labels.

     _i_t_e_m_I_n_f_o 'signature(object = "itemMatrix")'; returns the whole
          item information 'data.frame' including labels.

     _i_t_e_m_I_n_f_o<- '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.

     _l_e_n_g_t_h 'signature(x = "itemMatrix")'; returns the number of
          elements (rows) in the itemMatrix.

     _s_h_o_w 'signature(object = "itemMatrix")'

     _s_u_m_m_a_r_y 'signature(object = "itemMatrix")'

_A_u_t_h_o_r(_s):

     Michael Hahsler

_S_e_e _A_l_s_o:

     'transactions-class', 'itemsets-class', 'rules-class'

_E_x_a_m_p_l_e_s:

     ## 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")

