About the method "select" and "join"

Question

so I posted a question earlier about displaying factors of non-prime numbers and got this as a solution.

Below is a part of the code, but I have a little bit trouble understanding a few terms in them (since I am relatively new to ruby).

def factors(n)
   (1..n/2).select{|e| (n%e).zero?}.push(n)
 end

For instance,

What does the method select do in general?
What does .zero? do?

Then,

puts "#{n} is not a prime number =>#{factors(n).join(',')}"

What does .join(',') do?

It would be greatly appreciated if anyone can explain these terms to me in basic terms or simple concepts.

It would help if you could tell us, what *precisely* you don't understand about the documentation of those methods, so that the authors of the documentation can improve it. — Jörg W Mittag, Mar 03 '17 at 20:51

score 1 · Accepted Answer · answered Mar 03 '17 at 10:21

select method filters a collection. You specify the condition (the predicate) in the block and select returns items who match that condition.

[1,2,3,4].select(&:even?)
 => [2, 4]

i.zero? is another way to write i == 0

[0,2,3,0].select(&:zero?)
 => [0, 0]

join method concatenate a collection as a string with the parameter as a separators between items

[0,2,3,0].select(&:zero?).join(' and ')
 => "0 and 0"

Note

[1,2,3].select(&:even?)

is a simpler way to write

[1,2,3].select { |item| item.even? }

Dmitry Cat · Answer 2 · 2017-03-03T10:28:41.873

i will try explain by following links and text from documentation

join()

Returns a string created by converting each element of the array to a string, separated by the given separator. If the separator is nil, it uses current $,. If both the separator and $, are nil, it uses empty string.

[ "a", "b", "c" ].join        #=> "abc"
[ "a", "b", "c" ].join("-")   #=> "a-b-c"

select

Returns a new array containing all elements of ary for which the given block returns a true value.

If no block is given, an Enumerator is returned instead.

[1,2,3,4,5].select { |num|  num.even?  }   #=> [2, 4]

a = %w{ a b c d e f }
a.select { |v| v =~ /[aeiou]/ }  #=> ["a", "e"]

zero?

zero? → true or false
Returns true if num has a zero value.

Ruby html documentation: ruby-doc.org

Well, link-only answers are not useful. Either post as a comment, or elaborate, so that your answer still makes sense when/if links go dead. — Sergio Tulentsev, Mar 03 '17 at 10:23

About the method "select" and "join"

2 Answers2