Package 'FSInteract'

Random Intersection Trees

Description

Function to perform random intersection trees. When two binary data matrices z (class 1) and z0 (class 0) are supplied, it searches for interactions. More precisely, since the data matrices are binary, each row of each matrix can be represented by the set of column indices with non-zero entries. The function searches for sets (interactions) that are more prevalent in class 1 than class 0, and then sets that are more prevalent in class 0 than class 1. When given a single binary matrix z with the argument z0 omitted, the function simply finds sets with high prevalence. Prevalences of interactions returned are estimated using min-wise hashing.

Usage

RIT(z, z0, branch = 5, depth = 10L, n_trees = 100L,
    theta0 = 0.5, theta1 = theta0, min_inter_sz = 2L,
    L = 100L, n_cores = 1L, output_list = FALSE)

Arguments

z	data matrix where each row corresponds to an observation and columns correspond to variables. Can be in sparse matrix format (inherit from class "sparseMatrix" in the Matrix package).
z0	optional second data matrix with the same number of columns as z.
branch	average number of branches to use when creating each tree.
depth	maximum depth of trees.
n_trees	number of trees to be constructed.
theta0	when searching for sets of variables that are more prevalent in class 1 than class 0, the maximum threshold for prevalence in class 0.
theta1	as above but with class 1 and class 0 interchanged.
min_inter_sz	minimum size of the interactions to be returned
L	number of rows of the min-wise hash matrix used to estimate prevalences. A larger value will result in more accurate estimates, but computation time will increase linearly with L.
n_cores	number of cores for parallel processing. Only used when openMP is installed.
output_list	if FALSE returns each interaction set as a string with variable indices separated by spaces. If TRUE returns each interaction set as an integer vector.

Details

There are two tasks which can be performed with this function depending on whether or not z0 is supplied (note z must always be supplied).

1. If z0 is omitted, the function finds prevalent sets in z and theta0 and theta1 are ignored.

2. If z0 is supplied, it searches for sets that are prevalent in z but have prevalence at most theta0 in z0. Next sets that are prevalent in z0 but have prevalence in z at most theta1 are found.

Value

If output_list is FALSE (the default), the output is either a data frame (if z0 is omitted) or list of two data frames (if z0 is supplied). The data frames have first column a character vector of interaction sets with the variables in the sets separated by spaces, and second column the estimated prevalences. When z0 is supplied, the interactions in the first component of the list named Class1 are those which are prevalent in z and their prevalences in z are reported. The second component named named Class0 contains those interactions prevalent in z0 and their prevalences in z0.

When output_list is TRUE, each interaction is reported as an integer vector and so the collection of interactions is a list of such vectors.

Author(s)

Hyun Jik Kim, Rajen D. Shah

References

Shah, R. D. and Meinshausen, N. (2014) Random Intersection Trees. Journal of Machine Learning Research, 15, 629–654.

Examples

## Generate two binary matrices
z <- matrix(rbinom(250*500, 1, 0.3), 250, 500)
z0 <- matrix(rbinom(250*500, 1, 0.3), 250, 500)

## Make the first and second cols of z identical
## so the set 1, 2 has prevalence roughly 0.3 compared
## to roughly 0.09 for any other pair of columns
z[, 1] <- z[, 2]

## Similarly for z0
z0[, 3] <- z0[, 4]

## Market basket analysis
out1 <- RIT(z)
out1[1:5, ]

## Finding interactions
out2 <- RIT(z, z0)
out2$Class1[1:5, ]
out2$Class0[1:5, ]

## Can also perform the above using sparse matrices
if (require(Matrix)) {
  S <- Matrix(z, sparse=TRUE)
  S0 <- Matrix(z0, sparse=TRUE)
  out3 <- RIT(S, S0)
}

---