Map an array modifying only elements matching a certain condition

Question

In Ruby, what is the most expressive way to map an array in such a way that certain elements are modified and the others left untouched?

This is a straight-forw

Answer 1

It's a few lines long, but here's an alternative for the hell of it:

oa = %w| a b c |
na = oa.partition { |a| a == 'b' }
na.first.collect! { |a| a+'!' }
na.flatten! #Add .sort! here if you wish
p na
# >> ["b!", "a", "c"]

The collect with ternary seems best in my opinion.

Answer 2

old_a.map! { |a| a == "b" ? a + "!" : a }

gives

=> ["a", "b!", "c"]

map! modifies the receiver in place, so old_a is now that returned array.

Answer 3

Because arrays are pointers, this also works:

a = ["hello", "to", "you", "dude"]
a.select {|i| i.length <= 3 }.each {|i| i << "!" }

puts a.inspect
# => ["hello", "to!", "you!", "dude"]

In the loop, make sure you use a method that alters the object rather than creating a new object. E.g. upcase! compared to upcase.

The exact procedure depends on what exactly you are trying to achieve. It's hard to nail a definite answer with foo-bar examples.