In Ruby, Hashes haven't the map or map! method; it's for Arrays.

However, sometimes we need to do something with the keys or the elements of a Hash. Here I show some ways to do that:

1. Through each_key or each_pair (first natural options, from reference):

hash.each_key { |k| hash[k] = some_fun(hash[k]) }
hash.each { |k, v| hash[k] = some_fun(v) }
hash.each_pair { |k, v| hash[k] = some_fun(v) }

2. Through merge (inspired here):

hash.merge(hash) { |k, ov| sume_fun(ov) }

3. Here a way to modify the keys (from here):

Hash[*hash.map{|key,value| [key.upcase, value]}.flatten]

4. A way to work with hashes sorted by keys (which I published here):

hash.keys.sort.each { |k| puts k + " => " + hash[k] + "
\n" }

1. As I did in another post:

inc = lambda do |x|
 eval "#{x} += 1"
end

a = 5

inc[:a]

puts a #=> 6

2. Inspired here:

def inc(&blk)
 eval "#{yield} += 1", blk
end

x = 5
inc {:x}

puts x #=> 6

1. If you have a block of the form { |v| v.mtd }:

ary.each { |v| v.mtd } # normal way
ary.each(&:mtd) # simpler way

# Example:
ary = %w(abc def ghi jkl)
ary.each(&:upcase!) # same as ary.each { |v| v.upcase! }

That works for other Array methods, like map. More on it.

2. If you have a block of the form { |v| mtd v }, and the method mtd does the same thing with all parameters:

ary.each { |v| mtd v } # normal way
mtd *ary # simpler way

#Example:
ary = %w(abc def ghi jkl)
puts *ary # same as ary.each { |v| puts v }

See more on it.