Search an array for a string and its substrings in ruby

Question

I want to search an array for a certain string and(!) its substrings. For example my array is:

array = ["hello", "hell", "goodbye", "he"]

So when I search for "hello" and its substrings (but only from the beginning: "he", "hell", "hello"), it should return

=> ["hello", "hell", "he"]

What I've tried so far: Using a regular expression with the #grep and/or the #include? method like this:

array.grep("hello"[/\w+/])

or

array.select {|i| i.include?("hello"[/\w+/])}

but in both cases it only returns

=> ["hello"]

By the way, if I try array.select{|i| i.include?("he")} it works but like I said I want it the other way around: searching for "hello" and give me all results including the substrings from the beginning.

e is a substring of hello so goodbye should be in result. Or did you mean substrings only from beginning of the string? h,he,hel...hello? — Tom Gasaner
– Tom Gasaner, Commented Mar 10, 2015 at 16:17

steenslag · Accepted Answer · 2015-03-10 19:52:09Z

3

require "abbrev"

arr = ["hello", "hell", "goodbye", "he"]
p arr & ["hello"].abbrev.keys # => ["hello", "hell", "he"]

edited Mar 10, 2015 at 19:52

answered Mar 10, 2015 at 19:28

steenslag

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2 Comments

Wayne Conrad Over a year ago

That's just... beautiful

Cary Swoveland Over a year ago

That's very cool. I'd never heard of the module Abbrev, but considering it contains but a single method, I'm probably not alone. Those wanting more information (you can supply an optional pattern, for example) may wish to read this.

Tom Gasaner · Accepted Answer · 2015-03-10 16:30:58Z

2

array = ["hello", "hell", "goodbye", "he", "he"]

# define search word:
search = "hello"

# find all substrings of this word:
substrings = (0..search.size - 1).each_with_object([]) { |i, subs| subs << search[0..i] }
#=> ["h", "he", "hel", "hell", "hello"]

# find intersection between array and substrings(will exclude duplicates):
p array & substrings
#=> ["hello", "hell", "he"]

# or select array elements that match any substring(will keep duplicates):
p array.select { |elem| substrings.include?(elem) }
#=> ["hello", "hell", "he", "he"]

edited Mar 10, 2015 at 16:30

answered Mar 10, 2015 at 16:24

Tom Gasaner

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Comments

Arup Rakshit · Accepted Answer · 2015-03-13 19:47:36Z

2

I'd use String#[] :

array = ["hello", "hell", "goodbye", "he", "he"]
search = "hello"
array.select { |s| search[/\A#{s}/] }
# => ["hello", "hell", "he", "he"]

answered Mar 13, 2015 at 19:47

Arup Rakshit

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Comments

Avinash Raj · Accepted Answer · 2015-03-10 16:36:29Z

1

Turn all the characters other than h in hello to optional.

> array = ["hello", "hell", "goodbye", "he"]
> array.select{|i| i[/^he?l?l?o?/]}
=> ["hello", "hell", "he"]

answered Mar 10, 2015 at 16:36

Avinash Raj

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2 Comments

Cary Swoveland Over a year ago

Could my eyes be deceiving me? Is it possible that the regex-master got it wrong? ["hl"].select{|i| i[/^he?l?l?o?/]} #=> ["hl"].

Avinash Raj Over a year ago

Cary. Then he need to put hello,he'll,hel,he inside a non capturing group. Texting from my mobile so I can't able to add that.Regex master? no. I didn't get into that level.

engineersmnky · Accepted Answer · 2015-03-10 17:03:45Z

1

You could still use a regular expression like this

#define Array
arr = ["hello", "hell", "goodbye", "he"]
#define search term as an Array of it's characters
search = "hello".split(//)
#=> ['h','e','l','l','o']
#deem the first as manditory search.shift
#the rest are optional ['e?','l?','l?','o?'].join
search = search.shift << search.map{|a| "#{a}?"}.join
#=> "he?l?l?o?"
#start at the beginning of the string \A
arr.grep(/\A#{search}/)
#=> ["hello", "hell", "he"]

answered Mar 10, 2015 at 17:03

engineersmnky

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Comments

Cary Swoveland · Accepted Answer · 2015-03-10 18:08:46Z

1

Just as the question reads:

array.select { |w| "hello" =~ /^#{w}/ }
  #=> ["hello", "hell", "he"]

answered Mar 10, 2015 at 18:08

Cary Swoveland

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Comments

Darkmouse · Accepted Answer · 2015-03-10 16:21:59Z

0

Use array#keep_if

array = ["hello", "hell", he"]
substrings = array.keep_if{|a| a.start_with?('h')}
=> ["hello", "hell", "he"]

answered Mar 10, 2015 at 16:21

Darkmouse

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3 Comments

OhDaeSu Over a year ago

thanks, but isn't it the same as array.select{ |a| a.include?("h")} (in my example).

Darkmouse Over a year ago

Apparently it's not, because yours only returned "hello", mine returned what you were looking for. And also, include finds all elements that contain a string. start_with only finds strings that start with a string

Cary Swoveland Over a year ago

If array = ['hat'], 'hat' is returned, but 'hat' is not a substring of 'hello'.

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