Common operations on List objects
Description
Various functions and methods for looping on List objects, functional programming on List objects, and evaluation of an expression in a List object.
Usage
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44  ## Looping on List objects:
## 
## S4 method for signature 'List'
lapply(X, FUN, ...)
## S4 method for signature 'List'
sapply(X, FUN, ..., simplify=TRUE, USE.NAMES=TRUE)
endoapply(X, FUN, ...)
revElements(x, i)
mendoapply(FUN, ..., MoreArgs=NULL)
pc(...)
## Functional programming methods for List objects:
## 
## S4 method for signature 'List'
Reduce(f, x, init, right=FALSE, accumulate=FALSE)
## S4 method for signature 'List'
Filter(f, x)
## S4 method for signature 'List'
Find(f, x, right=FALSE, nomatch=NULL)
## S4 method for signature 'List'
Map(f, ...)
## S4 method for signature 'List'
Position(f, x, right=FALSE, nomatch=NA_integer_)
## Evaluation of an expression in a List object:
## 
## S4 method for signature 'List'
within(data, expr, ...)
## Constructing list matrices:
## 
## S4 method for signature 'List'
rbind(..., deparse.level=1L)
## S4 method for signature 'List'
cbind(..., deparse.level=1L)

Arguments
X, x 
A list, data.frame or List object. 
FUN 
The function to be applied to each element of 
... 
For For For For 
simplify, USE.NAMES 
See 
MoreArgs 
A list of other arguments to 
i 
Index specifying the elements to replace. Can be anything supported
by 
f, init, right, accumulate, nomatch 
See 
data 
A List object. 
expr 
Expression to evaluate. 
Details
Looping on List objects
Like the standard lapply
function defined in the
base package, the lapply
method for List objects
returns a list of the same length as X
, with each element being
the result of applying FUN
to the corresponding element of X
.
Like the standard sapply
function defined in the
base package, the sapply
method for List objects
is a userfriendly version of lapply
by default returning a vector
or matrix if appropriate.
endoapply
and mendoapply
perform the endomorphic equivalents
of lapply
and mapply
by returning
objects of the same class as the inputs rather than a list.
revElements(x, i)
reverses the list elements in x
specified
by i
. It's equivalent to, but faster than, doing
x[i] < endoapply(x[i], rev)
.
pc(...)
combines listlike objects in an elementwise fashion.
It's similar to, but faster than, mapply(c, ..., SIMPLIFY=FALSE)
.
With the following differences:

pc()
ignores the supplied objects that are NULL. 
pc()
does not recycle its arguments. All the supplied objects must have the same length. If one of the supplied objects is a List object, then
pc()
returns a List object.
pc()
always returns a homogenous list or List object, that is, an object where all the list elements have the same type.
Functional programming methods for List objects
The R base package defines some higherorder functions that are commonly
found in Functional Programming Languages.
See ?base::Reduce
for the details, and, in particular,
for a description of their arguments.
The S4Vectors package provides methods for List objects, so,
in addition to be an ordinary vector or list, the x
argument can
also be a List object.
Evaluation of an expression in a List object
within
evaluates expr
within as.env(data)
via
eval(data)
. Similar to with
, except assignments made
during evaluation are taken as assignments into data
, i.e.,
new symbols have their value appended to data
, and assigning
new values to existing symbols results in replacement.
Binding Lists into a matrix
There are methods for cbind
and rbind
that will bind
multiple lists together into a basic list matrix. The usual
geometric constraints apply. In the future, this might return a List
(+ dimensions), but for now the return value is an ordinary list.
Value
endoapply
returns an object of the same class as X
,
each element of which is the result of applying FUN
to the
corresponding element of X
.
mendoapply
returns an object of the same class as the first
object specified in ...
, each element of which is the result
of applying FUN
to the corresponding elements of ...
.
pc
returns a list or List object of the same length as the
input objects.
See ?base::Reduce
for the value returned by the
functional programming methods.
See ?base::within
for the value returned by
within
.
cbind
and rbind
return a list matrix.
Author(s)
P. Aboyoun and H. Pagès
See Also
The List class.

base::lapply
andbase::mapply
for the defaultlapply
andmapply
methods. 
base::Reduce
for the default functional programming methods. 
base::within
for the defaultwithin
method. 
base::cbind
andbase::rbind
for the default matrix binding methods.
Examples
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30  a < data.frame(x = 1:10, y = rnorm(10))
b < data.frame(x = 1:10, y = rnorm(10))
endoapply(a, function(x) (x  mean(x))/sd(x))
mendoapply(function(e1, e2) (e1  mean(e1)) * (e2  mean(e2)), a, b)
x < list(a=11:13, b=26:21, c=letters)
y < list((5:1), c("foo", "bar"), 0.25)
pc(x, y)
library(IRanges)
x < IntegerList(a=11:13, b=26:21, c=31:36, d=4:2)
y < NumericList((5:1), 1:2, numeric(0), 0.25)
pc(x, y)
Reduce("+", x)
Filter(is.unsorted, x)
pos1 < Position(is.unsorted, x)
stopifnot(identical(Find(is.unsorted, x), x[[pos1]]))
pos2 < Position(is.unsorted, x, right=TRUE)
stopifnot(identical(Find(is.unsorted, x, right=TRUE), x[[pos2]]))
y < x * 1000L
Map("c", x, y)
rbind(x, y)
cbind(x, y)

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