Enum#select with max number of items

Ruby
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

2

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

3

On Thu, Jan 24, 2013 at 10:08 PM, masta Blasta [email protected]
wrote:

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

4

Robert K. 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.

5

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.