Getting a substring in Ruby by x number of chars

Question

I'm trying to produce some Ruby code that will take a string and return a new one, with a number x number of characters removed from its end - these can be actual letters, numbers, spaces etc.

Ex: given the following string

a_string = "a1wer4zx"

I need a simple way to get the same string, minus - say - the 3 last characters. In the case above, that would be "a1wer". The way I'm doing it right now seems very convoluted:

an_array = a_string.split(//,(a_string.length-2))
an_array.pop
new_string = an_array.join

Any ideas?

It is convoluted, and, it's good that you had that feeling. Ruby in whole is an elegant language so when it feels like you're having to jump through hoops to do something, it's a warning you are probably going about it the wrong way. Of course there are going to be times that the solution is inelegant, because that's the nature of programming. Still, good Ruby really is zen-like, so go with the flow. :-) — the Tin Man, Dec 24 '10 at 23:25

score 126 · Accepted Answer · answered Dec 24 '10 at 19:45

126

How about this?

s[0, s.length - 3]

Or this

s[0..-4]

edit

s = "abcdefghi"
puts s[0, s.length - 3]  # => abcdef
puts s[0..-4]            # => abcdef

answered Dec 24 '10 at 19:45

Nikita Rybak

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Could someone explain what does s[0..-4] do? – Akshat Agarwal Dec 04 '15 at 18:00
1

I'm no expert, but it would certainly look like it wraps around the string. So doing `s[0..-1]` would return absdefgh. Usually `..` is used to represent a range – blastervla Jan 17 '18 at 13:33

score 16 · Answer 2 · answered Dec 24 '10 at 19:49

16

Use something like this:

s = "abcdef"
new_s = s[0..-2] # new_s = "abcde"

See the slice method here: http://ruby-doc.org/core/classes/String.html

answered Dec 24 '10 at 19:49

Brian Clapper

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score 8 · Answer 3 · answered Feb 23 '18 at 22:29

8

Another option could be to use the slice method

a_string = "a1wer4zx"
a_string.slice(0..5) 
=> "a1wer4"

Documentation: http://ruby-doc.org/core-2.5.0/String.html#method-i-slice

answered Feb 23 '18 at 22:29

Paulo Fidalgo

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Aray Karjauv · Answer 4 · 2017-08-03T18:55:04.093

3

if you need it in rails you can use first (source code)

s = '1234567890'
x = 4
s.first(s.length - x) # => "123456"

there is also last (source code)

s.last(2) # => "90"

alternatively check from/to

edited Aug 03 '17 at 18:55

answered Aug 03 '17 at 18:36

Aray Karjauv

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score 2 · Answer 5 · answered May 30 '17 at 21:38

2

Another option is getting the list of chars of the string, takeing x chars and joining back to a string:

[13] pry(main)> 'abcdef'.chars.take(2).join
=> "ab"
[14] pry(main)> 'abcdef'.chars.take(20).join
=> "abcdef"

answered May 30 '17 at 21:38

Leo Brito

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score 1 · Answer 6 · answered Aug 25 '22 at 16:48

I know a lot of people already said this, but I think the best option is this:

'abcdefg'[0..-4] # should return 'abcd'

Something important to realize is that the returned string is inclusive on both endpoints. A lot of string parsing methods (e.g., the java and javascript substring method) are inclusive on the first endpoint and exclusive on the last, but this is NOT the case with the above way.

'abcdefghijklm'[1..5] # returns 'bcdef'


// substring method in java or javascript returns 'bcde'

'abcdefghijklm'.substring(1, 5);

Getting a substring in Ruby by x number of chars

6 Answers6