Create comma separated array using each loop

Question

How can I create list of IP address with comma separated when using each loop?

ip_list = [];
hostnames.each do |host|
  puts host.ip  
end

I tried ip_list.join but that isn't working at all. I want all the host IP in a variable with comma seperated.

I want the output to be comma separated string.

Example:

puts ip_list
10.10.10.10, 10.10.10.11

hostnames is a database query. It has IP, name, id etc. I want to pick only IP and create a comma separated list. It prints IP correctly for each host but I just need to create a list — Robert
– Robert, Commented Aug 28, 2022 at 13:52
There is no comma separated list in Ruby :) What do you mean? What's your input? What's expected output? Please edit your question — mechnicov
– mechnicov, Commented Aug 28, 2022 at 13:55

Les Nightingill · Accepted Answer · 2022-08-30 20:45:32Z

3

I know you asked to use each but why not use collect? This gives you an array:

hostnames.collect(&:ip)

If you want a comma-separated list do:

hostnames.collect(&:ip).join(',')

If you need conditions in the iterator, you can use the longer block syntax:

hostnames.collect { |host|
  next unless host.name.match(/some_regex/)
  host.ip
}.compact # b/c otherwise you'll end up with some nil entries

edited Aug 30, 2022 at 20:45

answered Aug 28, 2022 at 13:56

Les Nightingill

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5 Comments

Marcus Ilgner Over a year ago

This. Internalising the functional programming concepts map/filter/reduce will get you very far. Less mutable state and fewer if/else constructs, too.

Robert Over a year ago

Need to use each loop because I have conditions in the loop.

spickermann Over a year ago

What do those conditions look like?

Les Nightingill Over a year ago

@Robert you can include conditions in the collect iterator. I used a shorthand syntax, but I edited my answer to show the longer syntax, with conditions

Sebastián Palma Over a year ago

You could use each_with_object to avoid compact.

ttanimichi · Accepted Answer · 2022-08-28 13:58:05Z

0

How about this? You can use Array#push.

ip_list = [];
hostnames.each do |host|
  ip_list.push host.ip  
end
p ip_list

Or, Array#map would be more useful.

ip_list = hostnames.map { |host| host.ip }
p ip_list

answered Aug 28, 2022 at 13:58

ttanimichi

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Comments

mechnicov · Accepted Answer · 2022-08-28 14:56:13Z

0

If you want to get new array based on the existing one and filter by condition at the same time, you can use filter_map (was introduced in Ruby 2.7)

If you wan to get string from array just use join

hostnames.filter_map { |hostname| hostname.ip if some.condition }.join(", ")

answered Aug 28, 2022 at 14:56

mechnicov

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