can map/collect return fewer values than are found in the target?

[Kelly Dwight Felkins]

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Is there a way for collect to return fewer items than the enumerable the
collect is running on? It looks to me like
map/collect will return at least one value for each item in the array --
I've seen examples of how to return more items, but
not less.

Is there a way to do this more succinctly:

VOWELS =3D %w{a e i o u}
items =3D %w{ a b c d e f g h i}
new_items =3D []
items.each do |item|
new_items << item unless VOWELS.include(item)
end
new_items

map/collect in ruby seems very similar to map in perl except that in perl
the block can return zero or more elements. Is there an method in ruby that
is similar to perl's map?

Thanks,

-Kelly

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[Logan Capaldo]

Is there a way for collect to return fewer items than the
enumerable the
collect is running on? It looks to me like
map/collect will return at least one value for each item in the
array --
I've seen examples of how to return more items, but
not less.

Is there a way to do this more succinctly:

VOWELS = %w{a e i o u}
items = %w{ a b c d e f g h i}
new_items = []
items.each do |item|
new_items << item unless VOWELS.include(item)
end
new_items

map/collect in ruby seems very similar to map in perl except that
in perl
the block can return zero or more elements. Is there an method in
ruby that
is similar to perl's map?

Thanks,

-Kelly

new_items = items.reject { |item| VOWELS.include?(item) }

or

new_items = items.select { |item| true unless VOWELS.include?(item) }

or

new_items = items.inject([]) { |list, item| list << item unless
VOWELS.include?(item); list }

 

[Marcel Molina Jr.]

Is there a way for collect to return fewer items than the enumerable the
collect is running on? It looks to me like
map/collect will return at least one value for each item in the array --
I've seen examples of how to return more items, but
not less.

Is there a way to do this more succinctly:

VOWELS = %w{a e i o u}
items = %w{ a b c d e f g h i}
new_items = []
items.each do |item|
new_items << item unless VOWELS.include(item)
end
new_items

map/collect in ruby seems very similar to map in perl except that in perl
the block can return zero or more elements. Is there an method in ruby that
is similar to perl's map?

Looks like you want Arry#select. In fact, take a look at the docs

----------------------------------------------------------- Array#select
array.select {|item| block } -> an_array
------------------------------------------------------------------------
Invokes the block passing in successive elements from _array_,
returning an array containing those elements for which the block
returns a true value (equivalent to +Enumerable#select+).

a = %w{ a b c d e f }
a.select {|v| v =~ /[aeiou]/} #=> ["a", "e"]

marcel

 

[Kent Sibilev]

items.inject([]){|a,i| a << i unless VOWELS.include?(i); a}

Kent.

 

[David Vallner]

The difference seems to be that Ruby's interpretation of map seems to be=20
stricter than Perl's, e.g. for one item in the original Array, there's=20
exactly one corresponding item in the result.

If you want a method with the behaviour similar to Perl's, you could do:

class Array
def pl_map(&block)
map(&block).compact.flatten
end
end

new_items =3D items.pl_map { | item | item if VOWELS.include(item) }

David Vallner

D=C5=88a =C5=A0tvrtok 09 Febru=C3=A1r 2006 02:18 Kelly Dwight Felkins nap=
=C3=ADsal:

 

[Robert Klemme]

new_items = items.select { |item| true unless VOWELS.include?(item) }

new_items = items.select { |item| not VOWELS.include?(item) }

robert

 

[Jeremy Henty]

Is there a way for collect to return fewer items than the enumerable
the collect is running on?

Strictly speaking, no (AFAIK), but it's easy to fake it. Use
Array#collect with a block that returns nil when you don't want an
element, then Array#compact the result.

Similarly, to get the effect of a block returning multiple values to
Array#collect, just have the block return an Array and then
Array#flatten the result.

Cheers,

Jeremy Henty