Change all array elements that contain a specific string

Question

array = ["Spam is bad", "Ham is good"]

I would like to select elements from an array that include (s) the word "good" and set the string to a new variable. How can i do this?

Answer 1

It is almost like you typed the name:

array.select {|s| s.include? "good"}

Here's the doc: http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-select

Answer 2

Since no answer yet gives you instructions on how to update a string in an array to a new value, here are a few options:

# Find every string matching a criteria and change them
array.select{ |s| s.include? "good" }.each{ |s| s.replace( "bad" ) }

# Find every string matching a pattern and change them
array.grep.replace( "bad" ).each{ |s| s.replace( "bad" ) }

# Find the first string matching a criteria and change it
array.find{ |s| s =~ /good/ }.replace( "bad" )

However, all of the above will change each instance of the string. For instance:

jon   = Person.new "Johnny B. Goode"
array = [ jon.name, "cat" ]
array.find{ |s| s =~ /good/i }.replace( "bad" )

p array #=> "bad"
p jon   #=> #<Person name="bad">  Uh oh...

- , , :

# Find the _first_ index matching some criteria and change it
array[ array.index{ |s| s =~ /good/ } ] = "bad"

# Update _every_ item in the array matching some criteria    
array[i] = "bad" while i = array.index{ |s| s =~ /good/i }

# Another way to do the above
# Possibly more efficient for very large arrays any many items
indices = array.map.with_index{ |s,i| s =~ /good/ ? i : nil }.compact
indices.each{ |i| array[i] = "bad" }

, , :

# Create a new array with the new values
new_array = array.map do |s|
  if s =~ /good/i  # matches "Good" or "good" in the string
    "bad"
  else
    s
  end
end

# Same thing, but shorter syntax
new_array = array.map{ |s| s =~ /good/i ? "bad" : s }

# Or, change the array in place to the new values
new_array = array.map!{ |s| s =~ /good/i ? "bad" : s }

Answer 3

There is also a special method for this:

array.grep(/good/)  # => ["Ham is good"]

With # grep, you can do a lot because it accepts regex ...

Answer 4

map! sounds like a good choice.

x = ['i', 'am', 'good']
def change_string_to_your_liking s
    # or whatever it is you plan to do with s
    s.gsub('good', 'excellente!')
end
x.map! {|i| i =~ /good/ ?  change_string_to_your_liking(i) : i}
puts x.inspect