Truncate string to the first n words

Question

What's the best way to truncate a string to the first n words?

Are you using just Ruby, or Ruby on Rails? – Andrew Grimm Jun 05 '11 at 03:50 — Andrew Grimm, Jun 05 '11 at 03:50

Tilo · Accepted Answer · 2018-01-18T22:07:15.270

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n = 3
str = "your long    long   input string or whatever"
str.split[0...n].join(' ')
 => "your long long"


str.split[0...n] # note that there are three dots, which excludes n
 => ["your", "long", "long"]

edited Jan 18 '18 at 22:07

answered Jun 04 '11 at 09:02

Tilo

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`str.split(/\s+/, n+1)[0...n].join(' ')` will improve performance. – sawa Jun 04 '11 at 10:11
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this will get the first 4 words, not 3. – Zack Xu May 15 '14 at 17:14
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@ZackXu Make sure you use the `...` range literal, not the `..` one. Three dots excludes the nth value. – user513951 May 15 '14 at 17:19
You're right about. I overlooked. Mea Cupla. For exactly this reason, I believe my solution below is better because it's more clear. – Zack Xu May 15 '14 at 21:26
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What about: `truncate(my_string, :length => 300, :separator => ' ')` 300 being the number of characters. You won't be able to choose the number of words but that's not so bad! – Nima Izadi Jul 23 '14 at 08:28
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shouldn't it be `my_string.truncate(300, separator: ' ')`? http://apidock.com/rails/String/truncate – Yo Ludke Jul 03 '15 at 12:57

score 9 · Answer 2 · edited May 23 '17 at 12:33

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You could do it like this:

s     = "what's the best way to truncate a ruby string to the first n words?"
n     = 6
trunc = s[/(\S+\s+){#{n}}/].strip

if you don't mind making a copy.

You could also apply Sawa's Improvement (wish I was still a mathematician, that would be a great name for a theorem) by adjusting the whitespace detection:

trunc = s[/(\s*\S+){#{n}}/]

If you have to deal with an n that is greater than the number of words in s then you could use this variant:

s[/(\S+(\s+)?){,#{n}}/].strip

edited May 23 '17 at 12:33

Community

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answered Jun 04 '11 at 09:10

mu is too short

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An improvement: `trunc = s[/(\s*\S+){#{n}}/]`. You don't need `strip`. – sawa Jun 04 '11 at 09:43
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@sawa: You could put that (and your version of the `split` approach) down as an answer, improvements and clarifications of existing answers are worthwhile. – mu is too short Jun 04 '11 at 18:06
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@GiangNguyen: In that case you could use `s[/(\S+(\s+)?){,#{n}}/].strip`. – mu is too short Oct 31 '13 at 19:10

Zack Xu · Answer 3 · 2014-05-16T12:45:33.727

You can use str.split.first(n).join(' ') with n being any number.

Contiguous white spaces in the original string are replaced with a single white space in the returned string.

For example, try this in irb:

>> a='apple    orange pear banana   pineaple  grapes'
=> "apple    orange pear banana   pineaple  grapes"
>> b=a.split.first(2).join(' ')
=> "apple orange"

This syntax is very clear (as it doesn't use regular expression, array slice by index). If you program in Ruby, you know that clarity is an important stylistic choice.

A shorthand for join is * So this syntax str.split.first(n) * ' ' is equivalent and shorter (more idiomatic, less clear for the uninitiated).

You can also use take instead of first so the following would do the same thing

a.split.take(2) * ' '

score 4 · Answer 4 · answered Apr 21 '15 at 22:22

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This could be following if it's from rails 4.2 (which has truncate_words)

string_given.squish.truncate_words(number_given, omission: "")

answered Apr 21 '15 at 22:22

kangkyu

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Truncate string to the first n words

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