How to return string with character at given index removed?

Question

I have a string, e.g.

string = 'foo-bar'

and I want a new string which doesn't contain the character at index 3 (the - in the example string), so the results would be "foobar". The former string must not be changed.

This is what I have so far:

new_string = string.dup
new_string.slice!(3)
new_string
#=> "foobar"

string
#=> "foo-bar"

or as a "one-liner":

new_string = string.dup.tap { |s| s.slice!(3) }
#=> "foobar"

But having to dup and maybe tap looks quite cumbersome. Is there a more concise way?

I don't know if such method exists already, but you can always create one, and hide the dup/tap there. — Sergio Tulentsev
– Sergio Tulentsev, Commented May 23, 2018 at 9:40
@SergioTulentsev I though that I might be overlooking an obvious solution. — Stefan
– Stefan, Commented May 23, 2018 at 9:42
Coincidentally there is a recent feature request for dup accepting a tap-like block. Not sure if that's a good idea though. — cremno
– cremno, Commented May 23, 2018 at 9:50
FYI I've opened a feature request for what I think would be a viable solution to my problem: bugs.ruby-lang.org/issues/14783 — Stefan
– Stefan, Commented May 23, 2018 at 10:24

Pascal · Accepted Answer · 2018-05-23 09:54:56Z

2

I'm not aware of such a method. You can write it yourself using slice though.

at = 3
string = "abc-def"
def delete_at(string, at)
  string.slice(0, at) + string.slice(at + 1, string.length)
end

x = delete_at(string, at) #> "abcdef"

You could also monkey patch it to String class (which I don't like though)

answered May 23, 2018 at 9:54

Pascal

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4 Comments

Stefan Over a year ago

Alternatively string[0...at] + string[at + 1..-1]

Pascal Over a year ago

@Stefan yes, that would work as well. I think that [] is way to overloaded though. So I never use it. ruby-doc.org/core-2.5.1/String.html#method-i-5B-5D

Stefan Over a year ago

String#[] and String#slice are aliases.

Pascal Over a year ago

@Stefan overloaded in the sense that it is used for lots of things e.g. accessing elements if an Array/Hash and my brain does not parse String[] well :-)

engineersmnky · Accepted Answer · 2018-05-23 19:10:35Z

1

Seems Kernel#sprintfcan solve this fairly simply:

str = "foo-bar"
sprintf("%3.3s%s",str,str[4..-1])
#=> "foobar"

Or simply

sprintf("%s%s",str[0..2],str[4..-1])
#=> "foobar"

Additionally Enumerable methods could help but seem a bit overkill e.g.

str.each_char.with_index.reduce("")  do |memo,(s,i)| 
  i == 3 ? memo : memo << s
end
#=> "foobar"

edited May 23, 2018 at 19:10

answered May 23, 2018 at 16:14

engineersmnky

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