dat (version 0.5.0)

map: An implementation of map

Description

An implementation of map and flatmap. They support the use of formulas as syntactic sugar for anonymous functions.

Usage

map(x, f, ...)
# S4 method for ANY,formula
map(x, f, ...)
# S4 method for atomic,`function`
map(x, f, ...)
# S4 method for list,`function`
map(x, f, p = function(x) TRUE, ...)
# S4 method for list,numericORcharacteORlogical
map(x, f, ...)
# S4 method for MList,`function`
map(x, f, ..., simplify = FALSE)
# S4 method for formula,`function`
map(x, f, ...)
flatmap(x, f, ..., flatten = unlist)
# S4 method for ANY,formula
flatmap(x, f, ..., flatten = unlist)
sac(x, f, by, ..., combine = bindRows)
# S4 method for data.frame,`function`
sac(x, f, by, ..., combine = bindRows)
# S4 method for ANY,formula
sac(x, f, by, ..., combine = bindRows)
vmap(x, f, ..., .mc = min(length(x), detectCores()), .bar = "bar")

Arguments

x

(vector | data.frame | formula) if x inherits from data.frame, a data.frame is returned. Use as.list if this is not what you want. When x is a formula it is interpreted to trigger a multivariate map.

f

(function | formula | character | logical | numeric) something which can be interpreted as a function. formula objects are coerced to a function. atomics are used for subsetting in each element of x. See the examples.

...

further arguments passed to the apply function.

p

(function | formula) a predicate function indicating which columns in a data.frame to use in map. This is a filter for the map operation, the full data.frame is returned.

simplify

see SIMPLIFY in mapply

flatten

(function | formula) a function used to flatten the results.

by

(e.g. character) argument is passed to extract to select columns.

combine

(function | formula) a function which knows how to combine the list of results. bindRows is the default.

.mc

(integer) the number of cores. Passed down to mclapply or mcmapply.

.bar

(character) see verboseApply.

Details

map will dispatch to lapply. When x is a formula this is interpreted as a multivariate map; this is implemented using mapply. When x is a data.frame map will iterate over columns, however the return value is a data.frame. p can be used to map over a subset of x.

flatmap will dispatch to map. The result is then wrapped by flatten which is unlist by default.

sac is a naive implementation of split-apply-combine and implemented using flatmap.

vmap is a 'verbose' version of map and provides a progress bar and a link to parallel map (mclapply).

map, flatmap, and sac can be extended; they are S4 generic functions. You don't and should not implement a new method for formulas. This method will coerce a formula into a function and pass it down to your map(newtype, function) method.

Examples

# NOT RUN {
# Sugar for anonymous functions
map(data.frame(y = 1:10, z = 2), x ~ x + 1)
map(data.frame(y = 1:10, z = 2), x ~ x + 1, is.numeric)
map(data.frame(y = 1:10, z = 2), x ~ x + 1, x ~ all(x == 2))
sac(data.frame(y = 1:10, z = 1:2), df ~ data.frame(my = mean(df$y)), "z")

# Trigger a multivariate map with a formula
map(1:2 ~ 3:4, f(x, y) ~ x + y)
map(1:2 ~ 3:4, f(x, y) ~ x + y, simplify = TRUE)
map(1:2 ~ 3:4, f(x, y, z) ~ x + y + z, z = 1)

# Extracting values from lists
map(list(1:2, 3:4), 2)
map(list(1:3, 2:5), 2:3)
map(list(1:3, 2:5), c(TRUE, FALSE, TRUE))

# Some type checking along the way
map(as.numeric(1:2), numeric : x ~ x)
map(1:2, integer(1) : x ~ x)
map(1:2, numeric(1) : x ~ x + 0.5)
# }