itertools2 (version 0.1.1)

ifilter: Iterator that filters elements not satisfying a predicate function

Description

Constructs an iterator that filters elements from iterable returning only those for which the predicate is TRUE.

Constructs an iterator that filters elements from iterable returning only those for which the predicate is FALSE.

Usage

ifilter(predicate, iterable)
ifilterfalse(predicate, iterable)

Arguments

predicate

a function that determines whether an element is TRUE or FALSE. The function is assumed to take only one argument.

iterable

an iterable object

Value

iterator object

Examples

# Filters out odd numbers and retains only even numbers
is_even <- function(x) {
  x %% 2 == 0
}
it <- ifilter(is_even, 1:10)
as.list(it)

# Similar idea here but anonymous function is used to filter out even
# numbers
it2 <- ifilter(function(x) x %% 2 == 1, 1:10)
iterators::nextElem(it2) # 1
iterators::nextElem(it2) # 3
iterators::nextElem(it2) # 5
iterators::nextElem(it2) # 7
iterators::nextElem(it2) # 9

is_vowel <- function(x) {
  x %in% c('a', 'e', 'i', 'o', 'u')
}
it3 <- ifilter(is_vowel, letters)
as.list(it3)
# Filters out even numbers and retains only odd numbers
is_even <- function(x) {
  x %% 2 == 0
}
it <- ifilterfalse(is_even, 1:10)
as.list(it)

# Similar idea here but anonymous function is used to filter out odd
# numbers
it2 <- ifilter(function(x) x %% 2 == 1, 1:10)
as.list(it2)

is_vowel <- function(x) {
  x %in% c('a', 'e', 'i', 'o', 'u')
}
it3 <- ifilterfalse(is_vowel, letters)
iterators::nextElem(it3) # b
iterators::nextElem(it3) # c
iterators::nextElem(it3) # d
iterators::nextElem(it3) # f
iterators::nextElem(it3) # g
# iterators::nextElem(it) continues through the rest of the consonants