How can I remove a numerical extension from an array of filenames? - arrays

Question

I want to remove the last 11 characters of strings inside of an array. The array is:
["cool.mp3?3829483927", "wow.mp3?3872947629", "woa.mp3?8392748308"]
I want to convert the strings to this:
["cool.mp3", "wow.mp3", "woa.mp3"]
Is there a method specifically for this in Ruby? I know of chop and chomp, but nothing that can access each string in an array.

Answer 1

TL;DR
There are lots of ways to transform your string, including #slice, #split, #sub, and #partition to name a few. What you're really missing is the Array#map method, which applies a method or block to each element of an array.
Partition Your Filenames
One way to modify your array elements is to map the Enumerable#partition method onto each element, which splits your filenames into an array of components. Ordinarily, this would return an array of arrays where each partitioned string is a sub-array, but you can have the #map block return just the components you want. In this case, what you want is the first element of each partitioned array.
This may sound complicated, but it's actually very simple. For example:
files = ['cool.mp3?3829483927', 'wow.mp3?3872947629', 'woa.mp3?8392748308']
files.map { |filename| filename.partition('?').first }
#=> ["cool.mp3", "wow.mp3", "woa.mp3"]
A Minified Version
If you value compactness over readability, you can get the same result as the solution above with:
files = %w(cool.mp3?3829483927 wow.mp3?3872947629 woa.mp3?8392748308)
files.map { |f| f.partition(??)[0] }
#=> ["cool.mp3", "wow.mp3", "woa.mp3"]

Answer 2

If you want what is before the first '?', do this :
arr.map{|thing| thing.split('?')[0]}

Answer 3

If it's always 11 chars you can do:
arr=["cool.mp3?3829483927","wow.mp3?3872947629", "woa.mp3?8392748308"]
new=arr.map{|thing| thing[0...-11]}

Answer 4

String::slice can take a regex as an argument, so you could extract the names that you want (rather than dropping the last 11 characters):
arr = ["cool.mp3?3829483927","wow.mp3?3872947629", "woa.mp3?8392748308"]
arr.map! {|x| x.slice(/\w+\.mp3/) }
#=> ["cool.mp3", "wow.mp3", "woa.mp3"]

Answer 5

If arr is your array of strings:
arr.map { |s| s[/[^?]+/] }
# => ["cool.mp3", "wow.mp3", "woa.mp3"]
The regular expression /[^?]+/ matches one or more characters that are not (^ at the beginning of the character class) question marks. This uses the methods Array#map and String#[].