mwhich: Expanded ``which''-like functionality.

Description

Implements which-like functionality for a big.matrix, with additional options for efficient comparisons executed in C++ rather than R; also works for regular numeric matrices without the memory overhead.

Usage

mwhich(x, cols, vals, comps, op = 'AND')

Arguments

a big.matrix (or a numeric matrix; see below).

cols

a vector of column indices or names.

vals

a list (one component for each of cols) of vectors of length 1 or 2; length 1 is used to test equality (or not equal), while vectors of length 2 are used for checking values in the range (-Inf and Inf are allowed). I

comps

a list of operators, including 'eq', 'neq', 'le', 'lt', 'ge' and 'gt'. If a single operator, it will be replicated length(testCol) times.

the comparison operator for combining the results of the individual tests, either 'AND' or 'OR'.

Value

a vector of row indices satisfying the criteria.

Details

To avoid the creation of massive vectors in R when doing comparisons, mwhich() executes column-by-column comparisons of values to the specified values or ranges, and then returns the row indices satisfying the comparison using the op operator. More advanced comparisons are then possible (and memory-efficient) in R by doing set operations (union and intersect, for example) on the results of multiple mwhich() calls. Note that NA is a valid argument in conjunction with 'eq' or 'neq', replacing traditional is.na() calls. And both -Inf and Inf can be used for one-sided inequalities. If mwhich() is used with a regular numeric matrix, we access the data directly, so there is no memory overhead. Interested developers might want to look at our code for this case, which uses a handy pointer trick in C++.

Examples

Run this code

x <- as.big.matrix(matrix(1:30, 10, 3))
x[,]
x[mwhich(x, 1:2, list(c(2,3), c(11,17)),
                   list(c('ge','le'), c('gt', 'lt')), 'OR'),]

x[mwhich(x, 1:2, list(c(2,3), c(11,17)), 
                   list(c('ge','le'), c('gt', 'lt')), 'AND'),]

# These should produce the same answer with a regular matrix:
y <- matrix(1:30, 10, 3)
y[mwhich(y, 1:2, list(c(2,3), c(11,17)),
                   list(c('ge','le'), c('gt', 'lt')), 'OR'),]

y[mwhich(y, 1:2, list(c(2,3), c(11,17)),
                   list(c('ge','le'), c('gt', 'lt')), 'AND'),]


x[1,1] <- NA
mwhich(x, 1:2, NA, 'eq', 'OR')
mwhich(x, 1:2, NA, 'neq', 'AND')

# Column 1 equal to 4 and/or column 2 less than or equal to 16:
mwhich(x, 1:2, list(4, 16), list('eq', 'le'), 'OR')
mwhich(x, 1:2, list(4, 16), list('eq', 'le'), 'AND')

# Column 2 less than or equal to 15:
mwhich(x, 2, 15, 'le')

# No NAs in either column, and column 2 strictly less than 15:
mwhich(x, c(1:2,2), list(NA, NA, 15), list('neq', 'neq', 'lt'), 'AND')

x <- big.matrix(4, 2, init=1, type="double")
x[1,1] <- Inf
mwhich(x, 1, Inf, 'eq')
mwhich(x, 1, 1, 'gt')
mwhich(x, 1, 1, 'le')