Adding to arrays based on names of elements in another array

Question

Couldn't find a less confusing title but here is the pseudo-code:

for all video['tags'][i] in video['tags'][3..-1]
  topic = video['tags'][i]
  topic_array += video['id']
end

Let's say there are 2 elements in the video['tags'][3..-1]:

video['tags'][3..-1] # => ["Health", "Politics"]
video['id']          # => 35

I want to add the integer 35 to two different arrays named Health and Politics. Those arrays may or may not exist beforehand.

End result example:

Health # => [21, 25, 35]
Politics # => [35]

Gerry · Accepted Answer · 2017-07-04 13:33:56Z

1

Instead of using multiple arrays to store ids for each tag, i would use one hash in which each key is a tag and its value is the array of ids, for example:

tags = { "Health" => [21, 25] }

With that in place, you could solve your problem with something like this:

video["tags"][3..-1].each do |tag|
  tags.key?(tag) ? tags[tag] << video["id"] : tags[tag] = [video["id"]]
end

Check for tags contents:

tags
#=> {"Health"=>[21, 25, 35], "Politics"=>[35]}

To get the ids, you simply fetch/read the key (i.e tag) you want from tags hash, for example:

tags["Health"]
#=> [21, 25, 35]

edited Jul 4, 2017 at 13:33

answered Jul 4, 2017 at 13:28

Gerry

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2 Comments

Emre Over a year ago

Thanks, but is my pseudo-code not realizable in Ruby?

Gerry Over a year ago

@Emre You can use a for loop (check this post), although its more idiomatic to use each; but you can't dynamically create variables, that's why another data structure (i.e Hash) is recommended.

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