reject nil values while appending to ruby array inside loop

Question

I have a loop inside which I am appending the result of the loop to an array. The code is like this

urls = []
series_id = [100,200,300,400]
series_id.each do |id|
  result_urls += iterate_id_and_get_urls(id)
end

def iterate_id_and_get_urls(id)
  #do something with id and maps it and returns its url which would result in an array
  #return that url array
end

But iterate_id_and_get_urls(id) can also return nil sometimes which would result nil to be appended in result_urls. How can I avoid that. I am looking for something like the below

result_urls += iterate_id_and_get_urls(id) unless nil?

result_urls += iterate_id_and_get_urls(id) unless iterate_id_and_get_urls(id) = nil — Hetal Khunti
– Hetal Khunti, Commented Nov 20, 2014 at 12:51
You can do result_urls.compact at the end which will remove all nil values — Kranthi
– Kranthi, Commented Nov 20, 2014 at 12:53
@HetalKhunti I can do like this result_urls += iterate_id_and_get_urls(id) unless iterate_id_and_get_urls(id) = nil. But that would make call to iterate_id_and_get_urls(id) twice, if I am not wrong.. — rubyist
– rubyist, Commented Nov 20, 2014 at 13:12

Uri Agassi · Accepted Answer · 2014-11-20 13:49:26Z

3

How about using flat_map:

result_urls = series_id.flat_map { |id| iterate_id_and_get_urls(id) }.compact

or even:

result_urls = series_id.flat_map { |id| iterate_id_and_get_urls(id) || [] }

answered Nov 20, 2014 at 13:49

Uri Agassi

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1 Comment

Boris Stitnicky Over a year ago

When I heard about flat_map, I thought to myself, this is like flatten, cool but not much use for it. You found a good usecase here, congrats.

Hetal Khunti · Accepted Answer · 2014-11-20 14:38:19Z

2

You can try something like

series_id.each do |id|
  if value = iterate_id_and_get_urls(id)
    result_urls += value.compact
  end
end

So nil url's will not get added to result_urls

Compact : Returns a copy of self with all nil elements removed.

edited Nov 20, 2014 at 14:38

Hetal Khunti

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answered Nov 20, 2014 at 12:46

Kranthi

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7 Comments

tejasbubane Over a year ago

use unless instead of if !

Boris Stitnicky Over a year ago

And also, is the conditional necessary at all if you use #compact?

Kranthi Over a year ago

#compact removes nil and returns empty array. In ruby [] is also evaluated as true. so #empty? returns true or false. based on that value gets appended to result_urls

Boris Stitnicky Over a year ago

Yes, but I suspect that if you drop it, the code will work anyway =)

Boris Stitnicky Over a year ago

Simple statement result_urls += value.compact will work, to be completely clear.

|

Boris Stitnicky · Accepted Answer · 2014-11-20 13:40:10Z

1

series_id.map( &method( :iterate_id_and_get_urls ) ).compact.reduce( [], :+ ).compact

edited Nov 20, 2014 at 13:40

answered Nov 20, 2014 at 13:26

Boris Stitnicky

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