Enum#select with max number of items

ruby-talk
1

My premise is that i have a large array that i'd like to iterate with
select, but
I want up to a maximum (n) number of returns. Something like
Enum#select_first_n_matches.

yes i could do my_arr.select{ blocky }.first(n). Which is a neat
one-liner, but has the performance overhead of iterating through the
entire array.

is there a method that does this already? Anyone have any slick one-line
solutions?

My working solution is:
new_arr = []; matches = 0
my_arr.each do |ele|
  if condition
     new_arr << ele
     matches += 1
     break if matches >= limit
  end
end

···

--
Posted via http://www.ruby-forum.com/.

2

Not sure about one-liners, but you can replace the matches integer with
new_arr.count / size / length

···

--
Posted via http://www.ruby-forum.com/.

3

My premise is that i have a large array that i'd like to iterate with
select, but
I want up to a maximum (n) number of returns. Something like
Enum#select_first_n_matches.

yes i could do my_arr.select{ blocky }.first(n). Which is a neat
one-liner, but has the performance overhead of iterating through the
entire array.

is there a method that does this already? Anyone have any slick one-line
solutions?

irb(main):003:0> 1_000_000.times.inject() {|a,x| a << x if x.odd?;
break a if a.size >= 10; a}
=> [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]
irb(main):004:0> 1_000_000.times.inject() {|a,x| x.odd? and a << x
and a.size >= 10 and break a; a}
=> [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

My working solution is:
new_arr = ; matches = 0
my_arr.each do |ele|
  if condition
     new_arr << ele
     matches += 1
     break if matches >= limit
  end
end

You can simplify that

new_arr =

my_arr.each do |ele|
  if condition
     new_arr << ele
     break if new_arr.size >= limit
  end
end

or

new_arr =

my_arr.each do |ele|
  condition and
     new_arr << ele and
     new_arr.size >= limit and
     break
end

Kind regards

robert

···

On Thu, Jan 24, 2013 at 10:08 PM, masta Blasta <lists@ruby-forum.com> wrote:

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

4

You could try out the lazy iterators in Ruby 2.0. The preview has been made available recently, and there are articles about this online already.

···

--
Matma Rex

5

Robert Klemme wrote in post #1093631:

or

new_arr =

my_arr.each do |ele|
  condition and
     new_arr << ele and
     new_arr.size >= limit and
     break
end

This is clever but is there a specific technical reason for using 'and'.
To me it makes it harder to read than conventional structure.

···

--
Posted via http://www.ruby-forum.com/\.