ergm (version 4.7.1)

For-ergmTerm: A for operator for terms

Description

This operator evaluates the formula given to it, substituting the specified loop counter variable with each element in a sequence.

Usage

# binary: For(...)

Arguments

...

in any order,

• one unnamed one-sided ergm()-style formula with the terms to be evaluated, containing one or more placeholders VAR and

• one or more named expressions of the form VAR = SEQ specifying the placeholder and its range. See Details below.

Details

Placeholders are specified in the style of foreach::foreach(), as VAR = SEQ. VAR can be any valid R variable name, and SEQ can be a vector, a list, a function of one argument, or a one-sided formula. The vector or list will be used directly, whereas a function will be called with the network as its argument to produce the list, and the formula will be used analogously to purrr::as_mapper(), its RHS evaluated in an environment in which the network itself will be accessible as . or .nw.

If more than one named expression is given, they will be expanded as one would expect in a nested for loop: earlier expressions will form the outer loops and later expressions the inner loops.

See Also

ergmTerm for index of model terms currently visible to the package.

ergm:::.formatTermKeywords("ergmTerm", "For", "subsection")

Examples

#
# The following are equivalent ways to compute differential
# homophily.
#

data(sampson)
(groups <- sort(unique(samplike%v%"group"))) # Sorted list of groups.

# The "normal" way:
summary(samplike ~ nodematch("group", diff=TRUE))

# One element at a time, specifying a list:
summary(samplike ~ For(~nodematch("group", levels=., diff=TRUE),
                       . = groups))

# One element at a time, specifying a function that returns a list:
summary(samplike ~ For(~nodematch("group", levels=., diff=TRUE),
                       . = function(nw) sort(unique(nw%v%"group"))))

# One element at a time, specifying a formula whose RHS expression
# returns a list:
summary(samplike ~ For(~nodematch("group", levels=., diff=TRUE),
                       . = ~sort(unique(.%v%"group"))))

#
# Multiple iterators are possible, in any order. Here, absdiff() is
# being computed for each combination of attribute and power.
#

data(florentine)

# The "normal" way:
summary(flomarriage ~ absdiff("wealth", pow=1) + absdiff("priorates", pow=1) +
                      absdiff("wealth", pow=2) + absdiff("priorates", pow=2) +
                      absdiff("wealth", pow=3) + absdiff("priorates", pow=3))

# With a loop; note that the attribute (a) is being iterated within
# power (.):
summary(flomarriage ~ For(. = 1:3, a = c("wealth", "priorates"), ~absdiff(a, pow=.)))