How do i invoke a method chain using map method, in ruby?

Question

How would I invoke the block to use _id.to_s in ruby?

category_ids = categories.map(&:_id.to_s)

I am hacking it and doing the following right now:

category_ids = []
categories.each do |c|
  category_ids << c.id.to_s
end

The documentation for [`Enumerable#map`](http://ruby-doc.org/core-1.9.3/Enumerable.html#method-i-map) shows how to use a block. Did you look at it? — the Tin Man, Feb 04 '13 at 16:15

score 13 · Accepted Answer · answered Feb 04 '13 at 15:48

13

You can pass a block to map and put your expression within the block. Each member of the enumerable will be yielded in succession to the block.

category_ids = categories.map {|c| c._id.to_s }

answered Feb 04 '13 at 15:48

Winfield

18,595
3
50
65

score 7 · Answer 2 · answered Feb 04 '13 at 16:32

7

category_ids = categories.map(&:_id).map(&:to_s)

Test:

categories = ["sdkfjs","sdkfjs","drue"]
categories.map(&:object_id).map(&:to_s)
=> ["9576480", "9576300", "9576260"]

answered Feb 04 '13 at 16:32

megas

20,851
11
74
129

jmjm · Answer 3 · 2020-01-09T15:18:02.097

If you really want to chain methods, you can override the Symbol#to_proc

class Symbol
  def to_proc
    to_s.to_proc
  end
end

class String
  def to_proc
    split("\.").to_proc
  end
end

class Array
  def to_proc
    proc{ |x| inject(x){ |a,y| a.send(y) } }
  end
end

strings_arr = ["AbcDef", "GhiJkl", "MnoPqr"]
strings_arr.map(&:"underscore.upcase")
#=> ["ABC_DEF", "GHI_JKL", "MNO_PQR"]

strings_arr.map(&"underscore.upcase")
#=> ["ABC_DEF", "GHI_JKL", "MNO_PQR"]

strings_arr.map(&["underscore", "upcase"])
#=> ["ABC_DEF", "GHI_JKL", "MNO_PQR"]

category_ids = categories.map(&"id.to_s")

Ruby ampersand colon shortcut

IRB

How do i invoke a method chain using map method, in ruby?

3 Answers3