Question

I want ‘This Is A 101 Test’ to be ‘This Is A Test’, but I can’t get the syntax right.

src = 'This Is A 101 Test'
puts "A) " + src                       # base => "This Is A 101 Test"
puts "B) " + src[/([a-z]+)/]           # only does first word => "his"
puts "C) " + src.gsub!(/\D/, "")       # Does digits, I want alphabetic => "101"
puts "D) " + src.gsub!(/\W///g)        # Nothing. => ""
puts "E) " + src.gsub(/(\W|\d)/, "")   # Nothing. => ""

Answer 1

First off, you need to be careful with gsub and gsub!. The latter is “dangerous!” and will modify the value of src. If you’re executing these statements in order, be aware that a.gsub!(/a/, "b") and a = a.gsub(/a/, "b") will both do the same thing to a. Part of the issue with your code is that src is being modified.

The B method returns "his" but makes no changes to source

src[/([a-z]+)/]     # => "his"
src                 # => "This Is A 101 Test"

The C method removes all characters that aren’t numbers:

src.gsub!(/\D/, "") # => "101"
src                 # => "101"

The D method doesn’t work because the syntax is wrong. The gsub method accepts a regular expression/string to search and then a string to use for replacement. If you try it in IRB it will act as though you need another / somewhere.

The E method replaces all non-word characters and all numbers:

src.gsub(/(\W|\d)/, "") # => "This Is A  Test" (note the two spaces)
src                     # => "This Is A 101 Test"

You point out that it’s returning "". Well, what’s actually happening is that C and D as listed (with syntax issues fixed) are destructive changes. (Also, if run on "101", D will actually return nil as no substitutions were performed.) So E is just being run on "101", and since you’re replacing all non-words and all numbers with "", it becomes "101".

---

The answer you’re looking for would be something like:

src.gsub!(/\d\s?/, "") # => "This Is A Test"
src                    # => "This Is A Test"

And my favorite for dealing with all scenarios of double spaces (because squeeze is quite efficient at combining like characters, strip is quite efficient at stripping trailing whitespace, and those ! return nil if they make no replacements):

src = src.gsub(/\d+/, "").squeeze(" ").strip