mirror of
https://github.com/nushell/nushell
synced 2024-12-27 05:23:11 +00:00
121 lines
3.1 KiB
Text
121 lines
3.1 KiB
Text
# | Filter Extensions
|
|
#
|
|
# This module implements extensions to the `filters` commands
|
|
#
|
|
# They are prefixed with `iter` so as to avoid conflicts with
|
|
# the inbuilt filters
|
|
|
|
# Returns the first element of the list that matches the
|
|
# closure predicate, `null` otherwise
|
|
#
|
|
# # Invariant
|
|
# > The closure has to be a predicate (returning a bool value)
|
|
# > else `null` is returned
|
|
# > The closure also has to be valid for the types it receives
|
|
# > These will be flagged as errors later as closure annotations
|
|
# > are implemented
|
|
#
|
|
# # Example
|
|
# ```
|
|
# use std ["assert equal" "iter find"]
|
|
#
|
|
# let haystack = ["shell", "abc", "around", "nushell", "std"]
|
|
#
|
|
# let found = ($haystack | iter find {|it| $it starts-with "a" })
|
|
# let not_found = ($haystack | iter find {|it| $it mod 2 == 0})
|
|
#
|
|
# assert equal $found "abc"
|
|
# assert equal $not_found null
|
|
# ```
|
|
export def "iter find" [ # -> any | null
|
|
fn: closure # the closure used to perform the search
|
|
] {
|
|
try {
|
|
filter $fn | get 0?
|
|
} catch {
|
|
null
|
|
}
|
|
}
|
|
|
|
# Returns a new list with the separator between adjacent
|
|
# items of the original list
|
|
#
|
|
# # Example
|
|
# ```
|
|
# use std ["assert equal" "iter intersperse"]
|
|
#
|
|
# let res = ([1 2 3 4] | iter intersperse 0)
|
|
# assert equal $res [1 0 2 0 3 0 4]
|
|
# ```
|
|
export def "iter intersperse" [ # -> list<any>
|
|
separator: any, # the separator to be used
|
|
] {
|
|
reduce -f [] {|it, acc|
|
|
$acc ++ [$it, $separator]
|
|
}
|
|
| match $in {
|
|
[] => [],
|
|
$xs => ($xs | take (($xs | length) - 1 ))
|
|
}
|
|
}
|
|
|
|
# Returns a list of intermediate steps performed by `reduce`
|
|
# (`fold`). It takes two arguments, an initial value to seed the
|
|
# initial state and a closure that takes two arguments, the first
|
|
# being the internal state and the second the list element in the
|
|
# current iteration.
|
|
#
|
|
# # Example
|
|
# ```
|
|
# use std ["assert equal" "iter scan"]
|
|
# let scanned = ([1 2 3] | iter scan 0 {|x, y| $x + $y})
|
|
#
|
|
# assert equal $scanned [0, 1, 3, 6]
|
|
#
|
|
# # use the --noinit(-n) flag to remove the initial value from
|
|
# # the final result
|
|
# let scanned = ([1 2 3] | iter scan 0 {|x, y| $x + $y} -n)
|
|
#
|
|
# assert equal $scanned [1, 3, 6]
|
|
# ```
|
|
export def "iter scan" [ # -> list<any>
|
|
init: any # initial value to seed the initial state
|
|
fn: closure # the closure to perform the scan
|
|
--noinit(-n) # remove the initial value from the result
|
|
] {
|
|
reduce -f [$init] {|it, acc|
|
|
$acc ++ [(do $fn ($acc | last) $it)]
|
|
}
|
|
| if $noinit {
|
|
$in | skip
|
|
} else {
|
|
$in
|
|
}
|
|
}
|
|
|
|
# Returns a list of values for which the supplied closure does not
|
|
# return `null` or an error. It is equivalent to
|
|
# `$in | each $fn | filter $fn`
|
|
#
|
|
# # Example
|
|
# ```nu
|
|
# use std ["assert equal" "iter filter-map"]
|
|
#
|
|
# let res = ([2 5 "4" 7] | iter filter-map {|it| $it ** 2})
|
|
#
|
|
# assert equal $res [4 25 49]
|
|
# ```
|
|
export def "iter filter-map" [ # -> list<any>
|
|
fn: closure # the closure to apply to the input
|
|
] {
|
|
each {|$it|
|
|
try {
|
|
do $fn $it
|
|
} catch {
|
|
null
|
|
}
|
|
}
|
|
| filter {|it|
|
|
$it != null
|
|
}
|
|
}
|