How do you replace a string with a hash collection value in Ruby?

Question

I have a hash collection: my_hash = {"1" => "apple", "2" => "bee", "3" => "cat"}

What syntax would I use to replace the first occurrence of the key with hash collection value in a string?

eg my input string: str = I want a 3

The resulting string would be: str = I want a cat

What assumptions are there about the input string? Generally, template languages like this mark it in some way, like str = I want a {3} (.NET string formatting). — Matthew Flaschen
– Matthew Flaschen, Commented Apr 9, 2012 at 22:32
Stack Overflow is not "please code this for me"; what is your code so far? What are your questions? — Phrogz
– Phrogz, Commented Apr 9, 2012 at 22:32
...apparently I'm wrong. As evidenced below, apparently we are all so desperate to help that we hand out code to new users. Welcome to Stack Overflow! ;) — Phrogz
– Phrogz, Commented Apr 9, 2012 at 22:41
I would use Ruby 2.0's built in string templating feature if at all possible. Given a hash with symbol keys, h = {pet: "cat"} you can do this: "I want a %{pet}" % h #=> "I want a cat" — Mark Thomas
– Mark Thomas, Commented Jun 10, 2014 at 21:09

Hauleth · Accepted Answer · 2014-01-20 09:54:51Z

21

My one liner:

hash.each { |k, v| str[k] &&= v }

or using String#sub! method:

hash.each { |k, v| str.sub!(k, v) }

edited Jan 20, 2014 at 9:54

answered Apr 9, 2012 at 22:36

Hauleth

23.7k4 gold badges67 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Phrogz Over a year ago

+1 (when I get the votes) for the useage of String#[]= and &&=.

San Over a year ago

Can some one explain what the first one liner does?

Hauleth Over a year ago

As boolean operators in Ruby are short-circuited the second argument is evaluated if and only if the first one is true. The String#[] if has given string it find it and return sub-string reference to it. So if we assign something to it we will change given part of the string. Finally we join it together and if sub-string is found in string then substitute it with hash value.

djoll Over a year ago

Lukasz, nice work. One correction: you need to use the 'sub!' method rather than the 'sub' method in order for your second example to work. 'sub!' alters the string in place. (Or use 'gsub!' to replace all occurrences of the match in the string.)

Karl Amort · Accepted Answer · 2016-10-24 01:40:37Z

17

"I want a %{b}" % {c: "apple", b: "bee", a: "cat"}
=> "I want a bee"

edited Oct 24, 2016 at 1:40

answered Mar 17, 2015 at 19:22

Karl Amort

16.4k8 gold badges69 silver badges77 bronze badges

Comments

Sergio Tulentsev · Accepted Answer · 2017-09-20 07:01:15Z

4

Assuming Ruby 1.9 or later:

str.gsub /\d/, my_hash

edited Sep 20, 2017 at 7:01

Sergio Tulentsev

231k43 gold badges381 silver badges373 bronze badges

answered Jun 10, 2014 at 20:49

smathy

28k5 gold badges51 silver badges70 bronze badges

Comments

fl00r · Accepted Answer · 2012-04-09 22:34:57Z

3

I didn't understand your problem, but you can try this:

my_hash = {"1" => "apple", "2" => "bee", "3" => "cat"}
str = "I want a 3"
str.gsub(/[[:word:]]+/).each do |word|
  my_hash[word] || word
end
#=> "I want a cat"

:D

answered Apr 9, 2012 at 22:34

fl00r

83.7k33 gold badges222 silver badges239 bronze badges

2 Comments

Hauleth Over a year ago

IMHO it's a little bit overloaded.

Phrogz Over a year ago

Heh, I like this one for turning my head upside down. (I'd +1 you, but I'm out for the day. ;)

Andrew Grimm · Accepted Answer · 2012-04-09 22:56:33Z

3

Just to add point free style abuse to fl00r's answer:

my_hash = {"1" => "apple", "2" => "bee", "3" => "cat"}
my_hash.default_proc = Proc.new {|hash, key| key}
str = "I want a 3"
str.gsub(/[[:word:]]+/).each(&my_hash.method(:[]))

answered Apr 9, 2012 at 22:56

Andrew Grimm

82.3k58 gold badges210 silver badges355 bronze badges

Comments

kxmh42 · Accepted Answer · 2012-11-25 23:46:35Z

2

my_hash = {"1" => "apple", "2" => "bee", "3" => "cat"}
str = "I want a 3"

If there isn't any general pattern for the strings you want to substitute, you can use:

str.sub /#{my_hash.keys.map { |s| Regexp.escape s }.join '|'}/, my_hash

But if there is one, the code becomes much simpler, e.g.:

str.sub /[0-9]+/, my_hash

If you want to substitute all the occurrences, not only the first one, use gsub.

answered Nov 25, 2012 at 23:46

kxmh42

3,8601 gold badge27 silver badges16 bronze badges

Comments

Oleksi · Accepted Answer · 2012-04-09 22:33:22Z

0

You can use String.sub in ruby 1.9:

string.sub(key, hash[key])

answered Apr 9, 2012 at 22:33

Oleksi

13.1k5 gold badges58 silver badges81 bronze badges

1 Comment

Matthew Hannigan Over a year ago

@Oleksi You meant hash not hash[key] i.e. my_hash = {"1" => "apple", "2" => "bee", "3" => "cat"} my_str = 'I want a 3' puts my_str.sub('3', my_hash) # => 'I want a cat'

Elmiya Agnes · Accepted Answer · 2017-09-20 10:08:36Z

0

The following code replace the first occurrence of the key with hash collection value in the given string str

 str.gsub(/\w+/) { |m| my_hash.fetch(m,m)}
    => "I want a cat"

edited Sep 20, 2017 at 10:08

answered Sep 20, 2017 at 5:58

Elmiya Agnes

2432 silver badges11 bronze badges

2 Comments

Nigel Ren Over a year ago

It would improve the quality of your answer if you could provide more of an explanation of what your code does. Why should someone try your code, is there something which can help them understand what they need to do?

Elmiya Agnes Over a year ago

explanation added

Collectives™ on Stack Overflow

How do you replace a string with a hash collection value in Ruby?

8 Answers 8

4 Comments

Comments

Comments

2 Comments

Comments

Comments

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

4 Comments

Comments

Comments

2 Comments

Comments

Comments

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related