How can I take out digits in each string? - ruby

Question

I'm trying to take out a number from each string and add 4 to each of them, but the compiler keeps telling me that:
undefined method `captures' for nil:NilClass (NoMethodError)
There is output 8 with the error message if I don't add match2 and int2 codes.
expecting output:
8
23
9
14
How can I fix this?
[
"I have 4 cucumbers",
"I've been given 19 radishes",
"I have 5 carrots in my hand",
"I gots 10 zucchini!"
].each do |string|
match = /^I have (\d) ([a-z]*)$/.match(string)
match2 = /I've been given (\d+) ([a-z]*)$/.match(string)
int = match.captures[0].to_i
int += 4
int2 = match2.captures[0].to_i
int2 += 4
puts int
puts int2
end

Answer 1

You can try this
array = []
[
"I have 4 cucumbers",
"I've been given 19 radishes",
"I have 5 carrots in my hand",
"I gots 10 zucchini!"
].each do |string|
array.push(string.scan(/\d+/))
end
new_array = array.flatten.map {|i| i.to_i}
#=> [4, 19, 5, 10]
new_array.map {|i| i.to_i + 4} #if you want to add 4 to each element
=> [8, 23, 9, 14]

Answer 2

It's not entirely clear what your expected output should be.
Meditate on this:
ary = ["a 4 b", "a 19 b"]
ary.each do |string|
string.gsub!(/\b\d+\b/) { |num| (num.to_i + 4).to_s }
end
ary # => ["a 8 b", "a 23 b"]
gsub! changes a string in place, whereas gsub returns the changed string. The difference would be:
ary = ["a 4 b", "a 19 b"]
new_ary = ary.map do |string|
string.gsub(/\b\d+\b/) { |num| (num.to_i + 4).to_s }
end
ary # => ["a 4 b", "a 19 b"]
new_ary # => ["a 8 b", "a 23 b"]
Notice that each became map, because we want to return an array of changed values, and gsub! because gsub.
It's important to use \b when searching for numbers in strings, otherwise you can run into problems with false-positive hits affecting digits inside "words" like "foo1".
If you want to return only the values after they've been incremented:
ary = ["a 0 b", "a 0 b 1"]
ary.map{ |a| a.scan(/\b\d+/).map{ |i| i.to_i + 4 }} # => [[4], [4, 5]]
Which, broken down, is doing this:
ary
.map{ |a|
a # => "a 0 b", "a 0 b 1"
.scan(/\b\d+/) # => ["0"], ["0", "1"]
.map{ |i| i.to_i + 4 } # => [4], [4, 5]
} # => [[4], [4, 5]]
In your code you're doing:
match = /^I have (\d) ([a-z]*)$/.match(string)
match2 = /I've been given (\d+) ([a-z]*)$/.match(string)
If you're processing freeform text you can't create a match for every possible incoming string; There are infinite possibilities. Even if you're in charge of the string creation, you shouldn't need to match entire strings, only specific parts. The more you try to match, the more likely it is the code will fail.