String delete method help

[Keith Johnston]

Hi,

I have a string which hold a URL. I'm trying to use the string .delete
method to remove the domain from the url but it isn't working as I
thought it should from the docs.

For example:

string = "http://groups.google.com/group/ruby-talk-google/"

I want to remove the "http://groups.google.com" part of the string, so
I tried:

string.delete('http', 'com')

thinking this would delete everything between 'http' and 'com' but all
I get is the entire string without any changes and with no errors.

I'm probably misunderstanding how the delete function works - can
someone explain?

Thanks,

 

[Stefano Crocco]

Alle Wednesday 01 October 2008, Keith Johnston ha scritto:

Hi,

I have a string which hold a URL. I'm trying to use the string .delete
method to remove the domain from the url but it isn't working as I
thought it should from the docs.

For example:

string = "http://groups.google.com/group/ruby-talk-google/"

I want to remove the "http://groups.google.com" part of the string, so
I tried:

string.delete('http', 'com')

thinking this would delete everything between 'http' and 'com' but all
I get is the entire string without any changes and with no errors.

I'm probably misunderstanding how the delete function works - can
someone explain?

Thanks,

There are two reasons for which your code doesn't do what you want:
* String#delete is a non-destructive method, that is it doesn't change its
receiver but creates a new string which is a copy of the receiver, modifies it
and returns it:

str = "abc"
str1 = str.delete 'a'
puts str
=> "abc"
puts str1
=> "bc"

If you want to modify the string in place, use String#delete!, instead

* String#delete removes from the string the characters which are the
intersection between its arguments. This means that a) it works character-
wise, so calling str.delete("abc") will delete all 'a', all 'b' and all 'c',
not just all instances of the substring 'abc'; b) in your case, the two
strings you pass to delete have no characters in common, so none will be
removed.

One way to do what you want is to use sub!:

string = "http://groups.google.com/group/ruby-talk-google/"
string.sub!("http://groups.google.com", '')

I hope this helps

Stefano

 

[Lars Haugseth]

Hi,

I have a string which hold a URL. I'm trying to use the string .delete
method to remove the domain from the url but it isn't working as I
thought it should from the docs.

For example:

string = "http://groups.google.com/group/ruby-talk-google/"

I want to remove the "http://groups.google.com" part of the string, so
I tried:

string.delete('http', 'com')

No need to reinvent the wheel:

require 'uri'
uri = URI.parse('http://groups.google.com/group/ruby-talk-google/')
puts uri.path

http://www.ruby-doc.org/stdlib/libdoc/uri/rdoc/classes/URI.html

 

[Keith Johnston]

Hi,

Yes, that helped. I was able to achieve what I thought the delete
function was doing by using String#sub! with a regular expression to
remove any charaters between "http" and "com".

string =3D "http://groups.google.com/group/ruby-talk-google/".sub!(/
http.*com/, "")


Thanks,

 

[David A. Black]

Hi --

Hi,

Yes, that helped. I was able to achieve what I thought the delete
function was doing by using String#sub! with a regular expression to
remove any charaters between "http" and "com".

string = "http://groups.google.com/group/ruby-talk-google/".sub!(/
http.*com/, "")

It's a bit dangerous to chain sub! (and, indeed, the ! means that this
is the dangerous version of sub, so it's always a good idea to check
the docs, since "danger" can mean many things).

str = "hello".sub!(/x/, 'y')
=> nil

That won't happen with your string but I'd still tend to steer clear
of assigning directly from a sub! call.


David

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