[RAILS] Ruby array manipulation

map Image that returns the id of a group with 5 or more people as an array

ids = groups.map{ |group| group.id if group.count >= 5}

#=> [1, 2, nil, 4,・ ・ ・]

Elements that do not meet the conditions will be nil

.reject(&:blank?) Eliminate nil and empty strings from arrays

ids = groups.map{ |group| group.id if group.count >= 5}.reject(&:blank?)

#=> [1, 2, 4,・ ・ ・]

filter_map Summarize the above. Available from Ruby 2.7

ids = groups.filter_map{ |group| group.id if group.count >= 5}

#=> [1, 2, 4,・ ・ ・]

join Returns a concatenated string. You can insert the character string in the argument

#=> "ABC"

#=> "A|B|C"

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